Bài Giảng Nhiệt Động Hóa Học - Giang Thị Kim Liên, Bài Giảng Động Hoá Học - Phạm Hữu Hùng, Mai Văn Bảy

8/11/2019 Bi Ging Nhit ng Ha Hc - Giang Th Kim Lin, Bi Ging ng Ho Hc - Phm Hu Hng, Mai Vn By

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I HC NNGTRNG I HC SPHM

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BI GING MN

Ngi son: Giang ThKim Lin

Nng, 2009


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CHNG 1. NGUYN L THNHT NHIT NG HC V P DNG VOHA HC (NHIT HA HC)

Nhit ng hc nghin cu dng nhit ca chuyn ng vt cht v nhng qui lutca chuyn ng . Nhit ha hc l mt phn ca nhit ng hc nhm mc ch kho

st strao i nng lng i km theo nhng bin i vt l, ha hc ca vt cht. Nhitha hc nghin cu mi lin hgia dng nhit v dng ha hc ca chuyn ng vt cht;gip tin on trong mt s trng hp mt bin i c th xy ra c hay khng; pdng nhng nh lut cbn ca nhit ng lc hc vo cc hin tng ha hc v c bitl cc hin tng ha l (cn bng ha hc, nh hng ca cc yu tkhc nhau n qutrnh ha hc, cc tnh cht nhit ng ca cc cht, cc h). Nghin cu vl thuyt dungdch; cu to v tnh cht dung dch ca cc cht khng in ly; quy tc pha..

I. MT SKHI NIM

1. Hnhit ng (Hthng - system)

Khi nim hnhit ng: Hnhit ng l mt phn ca vtrc gii hn xcnh ang c kho st vphng din trao i nng lng v vt cht, l tp hp camt sln cc tiu phn. Phn cn li ca vtrl mi trng ngoi i vi h. Hc thtrao i nng lng (nhit, cng) v vt cht vi mi trng ngoi.

V d: Mt bnh cha hn hp gm hai ha cht ang phn ng vi nhau. Hl cc

cht c mt trong bnh phn ng, gii hn ca hl thnh bnh, phn vtrngoi ng lmi trng ngoi.

Phn loi h:

+ Hh(hm): l hc thtrao i cnng lng ln vt cht vi mi trng ngoi.

V d: un si mt m nc, nhit c cung cp vo h, hmt vt cht ra mitrng ngoi di dng hi nc.

+ Hkn (hng): l hchtrao i nng lng vi mi trng ngoi nhng khng traoi vt cht vi mi trng ngoi. V d: hgm cc ha cht ang cho phn ng trongmt ng thy tinh hn kn. Hkhng mt vt cht nhng c thnhn nhit tmi trngvo (nu phn ng thu nhit) hoc cung cp nhit cho mi trng (nu phn ng ta nhit).


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+ Hc lp: l hkhng trao i cnng lng ln vt cht vi mi trng ngoi. V d:mt bnh cha ha cht c y kn v c bao phbng mt lp vt liu cch nhit cho vt cht v nhit lng khng thtrao i vi mi trng ngoi.

+ Hon nhit: C strao i cht nhng khng c strao i nhit vi mi trng.

+ Hng th: c tnh cht ng nht tt cmi im ca h.V d: kh nn trong bnh, ru cha trong chai...

+ Hdth: c tnh cht khng ng nht trong cc phn khc nhau ca hc phnchia vi nhau bng bmt vt l. V d, nc v nc 0oC...

+ Hvt l: hm trong xy ra cc qu trnh thay i vt l nhng khng c sthayi vbn cht ho hc. V d, sbin i cc trng thi vt cht nhit nng chy,

nhit si.

+ Hho hc: hm trong c mt phn hoc tt ccc thnh phn ho hc tc dng vinhau c sthay i vbn cht ho hc. V d, Zn v H2SO4 cha trong cc thutinh.

2. Trng thi v thng strng thi

Trng thi l mt tp hp trc tip hay gin tip ca cc thng strng thi, ni ln cim ca hang c kho st. Mt h c trng thi xc nh khi nhng thng s xcnh nhng i lng ca hc bit mt cch chnh xc nhnhit , thtch, p sut,khi lng ring... cc i lng ny c gi l thng strng thi ca h. Trng thi cahsthay i nu t nht c mt trong nhng thng strng thi thay i.

V d: 200cm3nc 25oC, 1atm cho bit trng thi ca hnc ang xt.

Ch trng thi y khc vi trng thi tp hp ca vt cht (pha, tng) l rn,lng, kh. V dhnc trn c un nng n 50oC, cng p sut 1atm th hny c trng thi khc: th tch nc ln hn 200cm3 mt t, nhit 50oC, p sut 1atm.Nhng trong chai trng thi ca hnc trn th nc ca hu pha lng.

Thng strng thi l cc i lng: nhit T, p sut P, thtch V, khi lng m,thnh phn ho hc... C 2 loi thng strng thi: thng sdung v thng scng :

* Thng sdung (khuch ):


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Thng sdung - tnh cht ca hvt cht c thtnh c tcc tnh cht cacc thnh phn tng ng cu to nn n, c gi trbng tng cc thng sca cc thnhphn. V d, khi lng phn tbng tng khi lng cc nguyn t; in tch ht nhnnguyn tbng tng in tch ca cc proton...

*Thng scng :Thng scng khng c tnh cng, khng phthuc vo yu tdung . V d, nhitca nc (cng ) khng phthuc vo thtch v khi lng ca n. Trang thi cn bng nhit ng:

Mt htrng thi cn bng nhit ng khi gi trca cc thng strng thi miim trong hu nhnhau v khng bin i theo thi gian hoc nu c bin i th bini v cng nh.

3. Qu trnh nhit ng (Bin i)

Mt hnhit ng hc bin i (hay thc hin mt qu trnh) khi trng thi ca hthay i. Trng thi ca hthay i nu t nht c mt thng strng thi ca hthay i.Bin i c xc nh nu bit r trng thi u v trng thi cui. Qu trnh c xcnh khi bit c trng thi u, trng thi cui v tt cnhng trng thi trung gian mh tri qua.

Phn loi cc loi qu trnh:

- Qu trnh h(m): l bin i m trng thi u v trng thi cui ca hkhc nhau.

V d: 200cm3nc 20oC, 1atm c un nng n 50oC, 1atm.

- Qu trnh kn (ng) - chu trnh: l bin i em httrng thi u n trng thi cuiging nhau.

V d: 200cm3nc 20oC, 1atm c un nng n 50oC, 1atm..ri li c lm nguiv20oC, 1atm.

- Qu trnh thun nghch: l bin i m cc trng thi trung gian ca htri qua c xemnhdo cc qu trnh cn bng. Mt cch n gin xc nh tnh cht thun nghch camt bin i l kho st xem bin i ngc li c thxy ra c hay khng khi chthayi rt t iu kin thc nghim. Nu bin i ngc xy ra c th l bin i thunnghch, nu bin i ngc khng xy ra c th l bin i bt thun nghch (hay bini tnhin).


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V d: struyn nhit tngun nng sang ngun lnh l mt bin i bt thun nghch haytnhin v bin i ngc li, tc s truyn nhit tngun lnh sang ngun nng khngththc hin mt cch tnhin. Sri tdo di tc dng ca trng trng cng l mtbin i tnhin hay bt thun nghch.

Sng c ca nc 0

o

C, 1atm l mt bin i thun nghch v bin i ngc li ngvi nc nng chy 0oC, 1atm cng c ththc hin c.

- Bin i ng tch: l bin i c thc hin trong iu kin thtch ca hkhng thayi.

V d: mt phn ng ha hc c thc hin trong ng hn kn.

- Bin i ng p: l bin i c thc hin trong iu kin p sut khng i.

V d: phn ng c thc hin trong bnh cu n thng vi kh quyn bn ngoi.

- Bin i ng nhit: l bin i c thc hin trong iu kin nhit khng i.

V d: phn ng c thc hin trong mt bnh cu nhc t trong bnh iu nhit(*)ginhit xc nh.

- Bin i on nhit: l bin i c thc hin trong iu kin khng c strao i nhitlng gia hvi mi trng ngoi.

V d: phn ng c thc hin trong bnh Dewar y kn, c bao quanh bi cc lpcch nhit tht dy.

4. Hm strng thi

Mt i lng c gi l hm strng thi ca hnu bin thin ca i lng chph

thuc vo trng thi u v trng thi cui ca hm khng phthuc vo cch tin hnhqu trnh (nhthun nghch hay bt thun nghch).

Ni chung, tt ccc thng strng thi ca hnhnhit T, p sut p, thtch V.... ul nhng hm strng thi ca hv nhng thng s chc trng cho trng thi angxt ca h. Khi h chuyn t trng thi u sang trng thi cui, bin thin ca nhngthng strng thi ca hchphthuc vo nhng trng thi , khng phthuc vo cctrng thi trung gian m htri qua.


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Mt bin thin hu hn (tng i ln) ca mt thng strng thi x trong qu trnh c

ghi l x = x2 - x1trong x1, x2l gi trca x trng thi u v trng thi cui.

Mt bin thin v cng nhca thng strng thi x sc ghi l dx hoc x

C nhng i lng khng phi l hm strng thi ca htrong trng hp tng qut nhnhit lng q, cng A. Nhit lng q v cng A m h trao i vi mi trng ngoikhng nhng ph thuc vo trng thi u, trng thi cui ca hm cn ph thuc vocch tin hnh qu trnh. Chng c trng cho qu trnh chkhng phi l thng strng

thi ca h. Chng ta qui c dng k hiu chnhng lng v cng nhca nhngi lng no khng phi l hm strng thi ca h, V d: v dng k hiu d hoc

cho nhng bin thin v cng nhca nhng thng sl hm strng thi ca h, V d:dT, dp, dV,...

5. Nhit v cng

Trong stng tc gia hvi mi trng ngoi c thc xy ra strao i nng lng.Khi c hai cch khc nhau trong schuyn nng lng tvt ny sang vt khc. Nu schuyn nng lng c lin quan n sthay i cng chuyn ng phn tca hthschuyn nng lng ny c thc hin di dng nhit. Nu schuyn nng lng clin quan n schuyn dch nhng khi lng vt cht vm di tc dng ca nhnglc no th schuyn nng lng ny c thc hin di dng cng.

V d: t nng mt hkh cha trong mt xy lanh kn th cc phn tkh sgiatngchuyn ng: h nhn nng lng di dng nhit. Kh gin ny piston (c khilng) i ln mt on: h cung cp ra mi trng ngoi nng lng di dng cng.Cn nu dng lc nn piston i xung mt on: h nhn nng lng t mi trngngoi di dng cng; cc phn tkh chuyn ng hn chtrong mt thtch nhhn nnc sva chm gia cc phn tkh nhiu hn v kt qul hnng ln: h cung cpnng lng cho mi trng ngoi di dng nhit.

Theo qui c vdu ca nhit ng hc:

- Nu hta nhit th nhit c trsm, q < 0.

- Nu hthu nhit th nhit c trsdng, q > 0.

- Nu hto cng th cng c trsm, W < 0.

- Nu hnhn cng th cng c trsdng, W > 0.


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a. Nhit

Nhit lng q cn dng em m gam ha cht tng ln mt khong nhit tng inhtT1 n T2 l:

q = mc(T2- T1)

Vi c l nhit dung ring) ca ha cht, l lng nhit cn em mt gam ha chttng ln mt , c xem nhkhng i trong khong nhit trn.

Thng ngi ta o nhit lng q p sut khng i hoc thtch khng i, lc t

nhit c sl tnhit ng p hoc tnhit ng tch .

Nu m = M, phn tgam (khi lng mol phn ttnh bng gam), th c tnhit mol ng

p hoc tnhit mol ng tch , l lng nhit cn em mt mol ha cht tng lnmt iu kin p sut khng i hoc thtch khng i.

Mcp= pMcV= V

Trn thc t, thng , thay i theo nhit . Trong trng hp ny, ngi ta xem

mt khong nhit tng i nh , trong tnhit mol trung bnh l v .

ng vi mt mol ha cht, ta c:

ln lt l nhit lng cn em mt mol ha cht tng ln iu kinng p, ng tch.

=>

Trstnhit mol ng p , tnhit mol ng tch ti nhit xt l:


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Vi n mol ha cht:

b. Cng

Ta thit lp biu thc tnh cng gin p ca h.

- Trng hp p sut ngoi khng i:

Xem mt hcha kh gin nnhhnh vtrn tthtch V1 n thtch V2. Gispistonc khi lng khng ng kv hchchu tc dng ca p sut ngoi khng i to nnbi s ln ca trng lng mg, vi m l khi lng ca mt vt nhc t trn b

mt piston, g l gia tc trng trng, S l tit din ca piston. p sut ngoi l:

Ghi ch: p sut l p lc tc dng ln mt n vdin tch. Lc p thng gc vidintch mt bp c gi l p lc.

Cng gin nca kh khi piston di chuyn ln mt on h l:

W = - mgh

(Cng = lc x on ng. Thm du - cng to c trsm)


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V2 - V1: tng thtch ng vi sdi chuyn ca piston ln mt on h.

Nu V2 - V1 > 0 => W < 0: hto cng

Nu V2 - V1 < 0 => W > 0: hnhn cng (nn piston i xung)

W < 0: cng gin nca hchng p sut ngoi.

W > 0: cng p, hnhn cng bi p sut ngoi ln.

Nu = 0 => W = 0 => Sgin nkh trong chn khng khng cung cp cng.

- Trng hp p sut ngoi thay i theo thtch V:

Trong trng hp ny ta xem mt on di chuyn nhdh ng vi mt tng thtch nhdV trong p sut ngoi c thxem nhkhng i.

Cng tng ng l:

[Dng k hiu (W v cng A khng phi l mt hm s trng thi, n thay i ty theong bin i]

Nu hcha kh l tng v bin i ng nhit, thun nghch, ta c:


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Ngoi ra ngi ta cng chng minh c rng cng gin nthun nghch l cng cc i(vtrstuyt i) cn cng cn cung cp nn p hmt cch thun nghch l cng cctiu (vtrstuyt i). Ngha l cng trng thi u, trng thi cui nhnhau, nu hginnthun nghch th cng to c trsm hn so vi cng gin nbt thun nghch.

Nu hbnn p thun nghch th cng cn cung cp t dng hn so vi bin i nn pbt thun nghch.

Do xt theo du i sth

II. NGUYN L THNHT NHIT NG HC. NI NNG U V ENTANPI H1. Nguyn l thnht nhit ng hc v ni nng U

Xem mt h bin i t trng thi (1) n

trng thi (2) theo nhiu ng bin i khcnhau. Gi q1, W1; q2, W2; ...; qi, Wi l nhitv cng trao i gia h vi mi trngngoi theo cc ng bin i 1, 2, ..., i.

Nguyn l thnht nhit ng hc c pht biu nhsau:

Nu qi v Wi l nhit v cng trao i gia hvi mi trng ngoi theo ngbin i i th qi v Wi ring rthay i theo ng bin i nhng tng sqi+Wi

lun lun l mt hng skhng ty thuc ng bin i m ch ty thuc votrng thi u v trng thi cui ca hm thi.

Q1 + W1 = q2 + W2 = .... = qi + Wi = const (hng s)

Vphng tin ton hc, biu thc trn chrng ta c thtm c mt hm snng lngU ca hnghim ng iu kin:

[Lu l nu qui c du ca cng A ngc vi gio trnh ny (nhtrong hu ht ccgio trnh ha l trc y), ngha l cng A m hnhn th c trsm, cn cng A mhto th c trsdng, th biu thc ca nguyn l thnht sl: = q - W ]

U2 v U1 ln lt l trsca U trng thi cui v trng thi u ca h.


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q v W l nhit v cng trao i gia hvi mi trng ngoi theo bt cng bin ino hi ttrng thi u n trng thi cui.

Hm sU ny biu din ni nng ca htc nng lng sn cha trong h.

[Ni nng ca hdo:

- ng nng chuyn ng phn t: tnh tin, quay, dao ng.

- Nng lng tng tc gia cc phn t: ht, y.

- Nng lng cc in ttrong phn t.

- Nng lng dtrca ht nhn nguyn t...]

ng vi mt bin i nh, ta c:

Ghi ch:

- Nguyn l thnht nhit ng hc chxc nh bin i ni nng chkhng thtnh c trstuyt i ca ni nng U.

- Nu hbin i ttrng thi (1) n trng thi (2) theo cc cch bin i thun nghchhay bt thun nghch, th trong cc cch bin i y u ging nhau. Cn q, W tri lic trskhc nhau ty theo cch bin i.

- Xem mt hbin i t trng thi (1) n trng thi (2) theo hai ng bin i khcnhau: mt thun nghch v mt bt thun nghch ta c:


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Ngha l nhit trao i cch bt thun nghch nhhn cch thun nghch theo i s.[Nhit m hnhn trong qu thun nghch ln hn so vi trong qu trnh bt thun nghchcn nhit m h ta ra trong qu trnh thun nghch nh hn so vi trong qu trnh btthun nghch ].

- Trong trng hp trng thi u v trng thi cui ging nhau, tc hthc hin mt chutrnh bin i kn, ta c:

Hthc ny l cch pht biu nguyn l tng ng:

Mt hbin i theo chu trnh kn v nu chc nhit v cng trao i gia hvi

mi trng ngoi, nu h thu nhit, n s to cng, nu hnhn cng, n s tonhit. Cng v nhit tng ng nhau.

[q > 0 W < 0; W > 0 q < 0; |w| = |q| ]

- Ngi ta chng minh rng i vi kh l tng, ni nng ca n chty thuc vo nhit.

Do , trong mt bin i ng nhit ca kh l tng khng c phn ng hahc,th bini ni nng

Cc phn ng ha hc thng c thc hin trong iu kin ng tch hay ng p.

2. Entalpi

a. Bin i ng tch.


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T: H = U + pV => H = U + nRT

=> Entalpi ca kh l tng chphthuc vo nhit T.

T (Tng qut q khng phi l hm strng thi, nhng iu kin ngtch th qV l hm strng thi).

M:

Vi n mol ha cht:

T: (Tng qut q khng phi l hm strng thi, nhng iu kin ng

p, qp l hm strng thi).

M:

Vi n mol ha cht:


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c. Hthc lin hgia vi ca kh l tng

Vi kh l tng:

III. KHO ST VI BIN I

1. Bin i ng nhit, thun nghch ca hkh l tng, chc cng gin p

T const

V bin i thun nghch


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(T const )

Nhvy vi hkh l tng, ng vi mt bin i ng nhit, thun nghch, chc cnggin p:

2. Bin i on nhit, thun nghch, kh l tng, chc cng gin p

(1.22)

Chia hai vcho :

=>


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m kh l tng:

(1.23)

Tm li: vi hkh l tng, bin i on nhit, thun nghch, chc cng gin p:


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BI TP CHNG 1

Cu hi.1. Thit lp biu thc ton hc ca nguyn l 1?2. Thit lp cng thc tnh cng v nhit cho qu trnh dn n ng nhit ca kh l

tng?3. Thit lp cng thc tnh cng v nhit cho qu trnh dn nng p v ng tch cakh l tng?

4. nh lut Hecxv cc hqu.5. Thit lp mi quan hgia nhit dung ng p v nhit dung ng tch?6. Khi nim entanpi. Mi quan hgia Qv v Qp?7. Sphthuc ca hiu ng nhit vo nhit . Phng trnh Kichp ?8. Thit lp quy tc tnh hiu ng nhit ca phn ng da vo sinh nhit v thiu nhit?9. Thit lp phng trnh on nhit cho kh l tng

Bi tp

Cu 1. Tnh U v H cho cc qu trnh sau y:a. Mt mol nc ng c 0oC v 1 atmb. Mt mol nc si 100oC v 1 atmBit rng: nhit ng c v nhit bay hi ca 1 mol nc tng ng bng -6,01 kJ v

40,79 kJ; thtch mol ca nc lng v nc bng 0,0180 lit v 0,0195 lit. Chp nhnhi l l tng.( R = 0,082 atm.l/K.mol ; p =1 atm = 101300 Pa ; 1atm.l = 101,3 J = 0,101kJ)

Cu 2. Nhit trung ho NaOH v dung dch NH3bng axit HCl tng ng l -55,9 v -51,34 kJ/mol. Xc nh nhit in ly ca amoniac.Cu3. Hiu ng nhit ca phn ng Na vi H2O (d) l H

01=-183,8 kJ/mol; ca phn

ng Na2O vi H2O (d) l H0

2= -237,9 kJ/mol. Bit: Hos,H2O = -285,8 kJ/mol.

Hy tnh H0298ca phn ng:2 Na + 1/2 O2 = Na2O

Cu4. Nhit hnh thnh ca Fe2O3(R) bng -821,3 kJ/mol; ca Al2O3bng -1675 kJ/mol.Tnh hiu ng nhit ca skh1 mol Fe2O3bng nhm kim loi.

Cu 5. Nhit trung ho axit HNO3 bng xt l 55,9 kJ. Cng lng dung dch xt trnc dng trung ho axit CHCl2COOH th hiu ng nhit nhn c bng -62,05 kJ.Nu cho 1 ng lng NaOH vo dung dch cha 1 ng lng HNO3 v 1 nglng CHCl2COOH th tora 58,4 kJ. Xc nh sng lng gam HNO3 phn ngvi NaOH.Cu 6. Nhit hnh thnh kh amoniac 298 K bng -46,2kJ/mol. Nhit dung mol ca H2,N2, NH3trong khong nhit 250-450 K c cho di y:


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CP, H2= 29,1 + 0,002 T J/mol.KCP, N2 = 27,1 + 0,006 T J/mol.KCP, NH3 = 25,9 + 0,032 T J/mol.K

Tnh H v U i vi phn ng to ra amoniac 398 K.Cu 7. Cho phn ng v cc sliu sau:

CH3OH(k) + 3/2 O2(k) = CO2(k) + 2 H2O (k)Ho298(KJ/mol) -201,2 0 -393,5 -241,8Cp (J/mol.) 49,4 29,4 37,1 33,6Tnh hiu ng nhit ca phn ng 500oK v 1atmCu 8. Nhit hnh thnh ca nc lng v ca CO2bng -285,8 v -393,5 kJ/mol 25

0C, 1atm, nhit t chy ca CH4 bng -890,3 kJ/mol. Tnh nhit hnh thnh ca CH4 t ccnguyn tiu kin ng p v ng tch.Cu 9.10 g kh O2l tng iu kin 298 K c nn on nhit tthtch 8 lit n 5lit. Xc nh nhit cui cng, cng tiu tn, U v H, bit CV= 5/2 R.

Cu 10. Tnh cng ca sbin i ng nhit thun nghch v bt thun nghch 42g khN2300K khi:

- gin nt5 atm xung 1 atm- nn t1 atm n 5 atm

Kh c coi l l tng, so snh kt qu..Cu 11. 25oC, phn ng sau: 2H2(k) + O2(k) = 2H2O(h)tora nhit lng l 483,66kJ trong iu kin p sut ring phn ca mi kh trong phnng l 1 atm v phn ng thc hin trong iu kin ng p. Nhit bay hi ca nc lng

25o

C, 1 atm l 44,01 kJ/mol.- Tnh nhit sinh chun ca H2O (l) v H2O (h) 25

oC.- Tnh nhit lng tora khi dng 6 g H2phn ng to thnh H2O(l).Cu 12. t chy mt lng xc nh C2H5OH(l) P = const = 1 atm v 273K trong scmt ca 22,4 m3O2tora 243 kJ.- Tnh smol C2H5OH dng bit rng sau phn ng cn li 5,6m

3O2ktc.- tnh nhit chy chun ca C2H5OH 273K.

- Tnh Ho273ca phn ng: C2H5OH (l) + O2 (k) = CH3COOH (l) + H2O (l)

Cu 13.Tnh Ho298v Uo298ca phn ng sau:

4Cgr + 3H2 + 2O2(k) = C4H6O4(r)Cho Ho298,C(kJ/mol) -393,51 -285,84 -1487

Cu 14.Phn ng:C6H6 + 15/2O2(k) = 6CO2(k) + 3H2O

300K c QP - QV = 1245J. Hi C6H6v H2O trong phn ng trng thi lng hay hi?

Cu 15.Tnh Ho473ca phn ng sau:


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CO(k) + 1/2 O2(k) = CO2(k)

cho bit Ho298,S ca CO(k) v CO2(k) ln lt l -110,52 v -393,51 kJ/mol; CoP

(J/mol.K) ca cc cht nhsau:CoP(CO) = 26,53 + 7,7.10

-3T - 1,17.10-6T2CoP(CO2) = 26,78 + 42,26,10-3T - 14,23.10

-6T2

CoP(O2) = 26,52 + 13,6.10

-3

T - 4,27.10-6

T2

Cu 16.Tnh Ho298,sca CH4(k), bit rng nng lng lin kt H-H trong H2l

436kJ/mol, nng lng lin kt trung bnh C-H trong CH4l 410kJ/mol v nhit nguyn t

ho Ho298,aca Cgrl:

Cgr --> C (k) , Ho298,s= 718,4 kJ/mol. Cc gi trtrn ly iu kin chun v 25oC.

Cu 17.Tnh nhit lng cn thit nng nhit ca 0,5mol nc t-50oC n 500oC P = 1 atm. Bit rng nhit nng chy ca nc 273K l 6004J/mol; nhit bay hi ca

nc 373K l 40660 J/mol; cc gi trnhit dung (J/mol.K ) l: CoP,R= 35,56; CoP,L=75,3 v CoP,H= 30,2 + 10

-2T.


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Chng 2. NGUYN L THHAI NHIT NG HC

V P DNG VO HA HC

Nguyn l th nht nhit ng hc gip xc nh bin i ni nng , bin i

entalpi ca mt qu trnh nhng ni chung khng gip don c qu trnh ny ctxy ra c hay khng. Nguyn l thhai nhit ng hc gip khng nh c iuny. p dng vo ha hc, nguyn l thhai nhit ng hc gip tin on mt phn ngha hc c thxy ra c hay khng mt iu kin xc nh no .

I. KHI NIM VENTROPI

Xem mt hgm cc phn tmt cht kh ang nhit thp, nu ta t nng h tccung cp mt nhit lng q vo, cc phn tkh sgia tng chuyn ng, c sxo trn

hay mt trt tnhiu trong hso vi trc khi cung cp q. Nhit lng q cng nhiu th sxo trn cng ln, tc sbin thin xo trn tlthun vi nhit lng q c cung cpvo h.

Nu cng mt lng nhit q nhng nu cung cp vo htrn ang nhit cao, th sbin thin xo trn st hn so vi lc hang nhit thp.

Nhvy sbin thin xo trn tlnghch vi nhit T.

Ngi ta dng mt hm strng thi o mc xo trn hay tdo ca mt h. lhm sentropi S m trong mt bin i nhc cho bi:

thun nghch l lng nhit c cung cp vo h mt cch thun nghch lm tng hm sentropi S ca hln mt lng dS hoc l lng nhit c ly ra khi h

mt cch thun nghch lm gim hm sentropi S ca hmt lng dS.

nhit khng i, vi mt bin i thun nghch xc nh:

Khi nhit T thay i:


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V l hm s trng thi, ging nh hm s ni nng U, hm s entalpi H, nn binientropi khng ty thuc ng bin i m chty thuc trng thi u v trngthi

cui ca hm thi.

Trong phm vi ha hc, hm sentropi c dng vi ngha c nh tdo camt hha hc.

Mt hbin i ttrng thi u n trng thi cui, vi trng thi cui t tdo hn trng

thi u th

Ngc li, nu trng thi cui tdo hn trng thi u th

V d:

II. PHT BIU NGUYN L THHAI NHIT NG HC

Nguyn l thhai nhit ng hc c thc pht biu nhsau:


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- Mi hc xc nh bng mt i lng gi l entropi S m bin i dS trong mt bini nhl:

Vi mt bin i xc nh ttrng thi (1) n trng thi (2), bin i entropi l:

qthun nghch l nhit trao i khi hbin i trong mt bin i nhtheo mtng bin i thun nghch.

Trong mt bin i ng nhit, thun nghch, bin i entropi l:

- Trong mt bin i thun nghch:

* Nu hc lp, th bin i entropi ca hl:

* Nu hkhng c lp th hcng mi trng ngoi to thnh mt hc lp, nn tng sbin i entropi ca hv ca mi trng ngoi bng khng.

- Trong mt bin i tnhin (bt thun nghch):

* Nu hc lp, th bin i entropi ca hdng:


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* Nu hkhng c lp th tng sbin i entropi ca hv ca mi trng ngoi dng.

III. CCH TNH BIN I ENTROPI

Hm sentropi S phthuc vo cc thng snhit T, thtch V hay p sut p.

S = S(T,V) hay S = S(T,p)

1. S = S(T,V)

- Vi bin i ng nhit To: (dT = 0)

- Vi bin i ng tch thtch khng i V0: (dV = 0)


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Nu tnhit mol ng tch khng i trong khong nhit (T1,T2):

2. S = S(T,p)

dS =

[Coi nhchc cng gin p]

dS =

Vi trng hp kh l tng:

- Vi bin i ng nhit T0:

- Vi bin i ng p p0:

Nu tnhit mol ng p khng i trong khong nhit (T1,T2):


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Ghi ch:

- p dng cc cng thc trn phi ch n cc iu kin thc hin bin i.

- Tuy iu kin thit lp cc cng thc trn l hkh l tng nhng cng c th pdng tnh bin i entropi cho ha cht trong iu kin thch hp khong nhit khng ln lm.

3. Cch tnh bin i entropi trong sthay i trng thi

a. Qu trnh nng chy:

Gi nhit nng chy ca ha cht l nhit ti c s cn bng pha giadng rn v dng lng ca ha cht di p sut 1 atm.

nhit nng chy mol ca ha cht, l nhit lng cncung cpmt mol ha cht

(A) t dng rn thnh dng lng nhit nng chy , p sut 1atm. ,

cng l nhit lng phng thch khi mt mol ha cht ng c tdng lng , 1atm).

b. Qu trnh bay hi:

Gi TS: nhit si (oK) ca ha cht (A), l nhit ti c scn bng pha gia dnglng v dng hi ca ha cht di p sut 1atm.


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S: nhit ha hi mol ca ha cht, l nhit lng cncung cp mt mol ha cht (A)

tdng lng thnh hi nhit si TSdi p sut 1atm. cng l nhit lngphng thch khi mt mol A dng hi ngng tthnh dng lng TS, 1atm).

y l mt bin i ng nhit, ng p, thun nghch.

IV. NGUYN L THBA NHIT NG HC. ENTROPI CA HA CHT

1. Nguyn l thba nhit ng hc

"Entropi ca mt tinh thhon ho bng khng 0oK"

Tinh thhon ho l tinh thtrong cc phn tchc mt cch sp xp duy nht 0oK.Nhiu ha cht c tinh thkhng hon ho 0oK nhH2(orto, para), CO, N2O, H2O...

Nguyn l thba nhit ng hc gip tnh entropi ca mt ha cht nhit xc nh.

2. Cch tnh bin i Entropi ca mt ha cht

Xt hai trng hp sau y:

a. Khng c sthay i trng thi trong khong nhit (0, T)

Nu chn v tinh thcht thuc loi hon ho


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V tnhit mol ng p phthuc nhit T, ta vng biu din ca hm s

theo thng s

b. C sthay i trng thi trong khong nhit (0, T)

=


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Tth, o cc din tch , cng li sbit c entropi mol ca ha cht

nhit ToK.

Da vo cch tnh , c thtnh c entropi mol ca ha cht mt nhit xc nh(nhit ti ha cht cha bphn hy).

Sau y l trsentropi mol iu kin chun thc (298 K, 1atm) ca mt sha cht

Ha cht 0298 K Ha cht0

298 K

J/mol.K cal/mol.K J/mol.K cal/mol.K

Ag(r)

AgCl(r)

Al(r)

Al2O3(r)

C(r,graphit)

CO(k)

CO2(k)

CH4(k)

CH3Cl(k)

CH3OH(l)

CO(NH2)2(r,ure)C2H2(k)

C2H4(k)

C2H6(k)

42,55

96,20

28,30

51,00

5,69

197,90

213,60

186,20

234,20

126,80

104,60200,80

219,80

229,50

10,17

23,00

6,77

12,19

1,36

47,30

51,06

44,50

55,97

30,30

25,0048,00

52,54

54,85

H2O(k)

H2O(l)

HCl(k)

HNO3(l)

H2SO4(l)

CH3COOH(l)

Hg(l)

Hg(k)

K(r)

KCl(r)

K2SO4(r)N2(k)

NH3(k)

NH4Cl(r)

188,70

69,96

186,70

155,60

157,00

160,00

76,10

175,00

64,18

82,59

176,00191,50

192,50

94,60

45,11

16,72

44,62

37,19

37,50

38,20

18,20

41,80

15,34

19,74

42,0045,77

46,01

22,60


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30

C2H5OH(l)

Ca(r)

CaCO3(r)

CaCl2(r)

CaO(r)

Ca(OH)2(r)

CaSO4(r)

CaSO4.2H2O(r)

Cl2(k)

Fe(r)

Fe2O3(r)

H2(k)

S(r)

C(r,kim cng)

161,00

41,40

92,90

114,00

40,00

76,10

107,00

194,00

223,00

27,00

90,00

130,60

31,90

2,40

38,40

9,89

22,20

27,20

9,50

18,20

25,50

46,36

53,29

6,50

21,50

31,21

7,62

0,57

NO(k)

NO2(k)

N2O(k)

N2O4(k)

Na(r)

Na2CO3(r)

NaHCO3(r)

NaCl(r)

NaOH(r)

Na2SO4(r)

O2(k)

PbO(r)

SO2(k)

SO3(k)

210,60

240,50

220,00

304,00

51,00

136,00

102,00

72,38

64,18

149,40

205,00

67,80

248,50

256,20

50,34

57,47

52,58

72,70

12,20

32,50

24,40

17,30

15,34

35,70

49,00

16,20

59,40

61,24

[Theo sch "Fundamentals of Chemistry" ca James E.Brady v John R.Holum (ti bn ln3, nm 1988)]

Nhn xt:

- Cng trng thi nhnhau (rn, lng hoc kh), cht no c cu to

phc tp hn th c trs ln hn.

p dng bng tr s entropi mol chun thc ca cc cht ta c th tnh c bin ientropi ca mt phn ng iu kin chun thc.


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Vi phn ng:

mA + nB -> pC + qD

V d1:

V d2:

[Ph hp vi don, v bn sn phm c 1 mol kh trong khi bn tc cht c 2 mol khinn t c sxo trn hn].

3. Bin i ca bin i Entropi theo nhit

Bit nhit To, tnh nhit T ca mt phn ng.

Xem phn ng: mA + nB -> pC + qD

T(2.17) =>

2.26


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Nu T0 l nhit iu kin chun thc (298 K) v nu p sut l 1atm, th:

Nu khng i theo nhit T trong khong (298 K, T) th:


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CHNG 3. THNHIT NG THHA HC

IU KIN CN BNG V DIN BIN CA QU TRNH

I. HM NNG LNG TDO G (THNG NHIT NG P, HM GIBBS)1. Hm snng lng tdo v bin i

Trn nguyn tc nu tnh c ca hv ca mi trng ngoi km theo mtbin i th ta c thxc nh bin i c xy ra tnhin (bt thun nghch) hay khng.Tuy nhin, sxc nh ca mi trng ngoi khng phi lc no cng ddng do ngi ta tm cch da trn chnh hkho st kt lun.

Mt hc khuynh hng bin i tnhin (bt thun nghch) khi tha mn hai iukin sau y:

- iu kin v hay : mt bin i c khuynh hng xy ra nu ta nhit( , ty iu kin th nghim ng p hay ng tch).

- iu kin v : mt bin i c khuynh hng xy ra nu c s tng entropi ca h( ).

Vy iu kin u i mt bin i p, T khng i l . Tuy nhin,c trng hp (thu nhit) hoc (gim entropi ca h), bin i cng c thxy ra c, nu yu tcn li ln p hn (tc trong trng hp bin i thu nhit

v trong trng hp c sgim entropi ca h).

Mt hm s trng thi c chn gp hai iu kin trn li, l hm snnglng tdo G, c nh ngha nhsau:

=> dG = dH - TdS - SdT

iu kin ng p:

iu kin ng nhit: dT = 0

3.1


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Cc bin i xy ra theo hai trng hp:

a- Nu bin i thun nghch:

Vi mt bin i xc nh:

b- Nu bin i bt thun nghch (bin i tnhin):

(2.31)

Vi mt bin i xc nh:

Tm li:

Vi biu thc trn, c thkt lun l mt bin i c thxy ra tnhin nu mt trong batrng hp sau y c tha (T, p khng i):

Cba trng hp trn trong thc tu c ghi nhn.

[ Ngi ta chng minh c: gim hm sG T, p khng i bng vicng thun nghch m h to cho mi trng ngoi, khng kcng lm thay i thtchca h, cng ny c thc sdng ty nghi, nn c gi l nng lng tdo ].

3.2

3.3

3.4

3.5


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2. Vi phn ca hm thng nhit ng p G

Tbiu thc G = H - TS

=> dG = dH - TdS - SdT (2.36)

m H = U + pV

=> dH = dU + pdV + Vdp

(Coi nhchc cng gin p)

(2.36) => dG = TdS + Vdp - TdS - SdT

3. Bin i ca nng lng tdo theo nhit v p sut

a. Bin i ca nng lng tdo theo p sut iu kin ng nhit

TdG = Vdp - SdT

iu kin ng nhit: dT = 0

=> dGT= Vdp

Vi kh l tng:

3.6

3.7


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(2.39)

[Cng thc trn p dng cho kh l tng, nhng c thp dng cho ha cht vi iu kinnhit T, ha cht trng thi kh v coi nh l kh l tng].

Nu p1 = 1 atm

Vi 1 mol:

[p: p sut, tnh bng atm. Ty theo th nguyn ca R mT c th nguyn thch hptng ng].

b. Bin i ca G theo nhit iu kin ng p

G = H - TS

3.8

3.9


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Trong mt phn ng ha hc:

mA + nB -> pC + qD

Theo kt quchng minh trn:

3.10


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=>

y l h thc Gibbs - Helmholtz, h thc ny gip tnh bt cnhit no iu

kin ng p, khi bit mt nhit xc nh v bit ca qu trnh.

4. Nng lng tdo mol chun

c thtnh bin thin trong mt bin i, ngi ta cng chn trng thi chunnhtrng hp entalpi. Trng thi chun ca mt ha cht l dng bn nht ca ha cht 25oC, 1atm. V d trng thi chun thc ca carbon (25oC, 1atm) l carbon graphit(than ch), chkhng phi l carbon kim cng.

Ngi ta qui c, nng lng tdo ca n cht trng thi chun bng khng.

Da vo qui c ny, ngi ta xc nh c nng lng t do mol chun ca cc hp

cht. Nng lng tdo mol chun c biu din bng k hiu .

V d:

3.11

3.12


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M:

Tnh c

[Cn cvo trsentalpi mol chun v entropi mol chun ca cc cht]

ThT = 298 K

Tnh c

Di y l trsnng lng tdo mol chun ca mt scht

Ha cht298 K

Ha cht298 K

KJ/mol Kcal/mol KJ/mol Kcal/mol

Ag(r)

AgCl(r)

Al(r)

Al2O3(r)

C(r,graphit)

CO(k)

CO2(k)

CH4(k)

CH3Cl(k)

CH3OH(l)CO(NH2)2(r)

CO(NH2)2(aq)

C2H2(k)

0,00

- 109,70

0,00

- 1576,40

0,00

- 137,30

- 394,40

- 50,79

- 58,60

- 166,20- 197,20

- 203,80

+ 209,00

0,00

- 26,22

0,00

- 376,77

0,00

- 32,81

- 94,26

- 12,14

- 14,00

- 39,73- 47,12

- 48,72

+ 50,00

H2O(k)

H2O(l)

HCl(k)

HNO3(l)

H2SO4(l)

CH3COOH(l)

Hg(l)

Hg(k)

K(r)

KCl(r)K2SO4(r)

N2(k)

NH3(k)

- 228,60

- 237,20

- 95,27

- 79,91

- 689,90

- 392,50

0,00

+ 31,80

0,00

- 408,30- 1316,40

0,00

- 16,70

- 54,64

- 56,69

- 22,77

- 19,10

- 164,90

- 93,80

0,00

+ 7,59

0,00

- 97,59- 314,62

0,00

- 3,98


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40

C2H4(k)

C2H6(k)

C2H5OH(l)

C8H18(l)

Ca(r)

CaCO3(r)

CaCl2(r)

CaO(r)

Ca(OH)2(r)

CaSO4(r)

CaSO4.1/2H2O(r)

CaSO4.2H2O(r)

Cl2(k)

Fe(r)

Fe2O3(r)

H2(k)

+ 68,12

- 32,90

- 174,80

+ 17,30

0,00

- 1128,80

- 750,20

- 604,20

- 896,76

- 1320,30

- 1435,20

- 1795,70

0,00

0,00

- 741,00

0,00

+ 16,28

- 7,86

- 41,77

+ 4,14

0,00

- 269,78

- 179,30

- 144,40

- 214,33

- 315,56

- 343,02

- 429,19

0,00

0,00

- 177,10

0,00

NH4Cl(r)

NO(k)

NO2(k)

N2O(k)

N2O4(k)

Na(r)

Na2CO3(r)

NaHCO3(r)

NaOH(r)

NaCl(r)

Na2SO4(r)

O2(k)

PbO(r)

S(r)

SO2(k)

SO3(k)

- 203,90

+ 86,69

+ 51,84

+ 103,60

+ 98,28

0,00

- 1048,00

- 851,90

- 382,00

- 384,00

- 1266,80

0,00

- 189,30

0,00

- 300,40

- 370,40

- 48,73

+ 20,72

+ 12,39

+ 24,76

+ 23,49

0,00

- 250,40

- 203,60

- 91,40

- 94,79

- 302,78

0,00

- 45,25

0,00

- 71,79

- 88,52

[ Theo sch Fundamentals of Chemistry ca James E. Brady v John R. Holum, ti bn ln3 - nm 1988 ]

II. P DNGNNG LNG TDO CHUN

C thp dng bng trsnng lng tdo mol chun thc ca ha cht tnh

c bin i nng lng tdo ca mt qu trnh iu kin chun thc . Hoc c

th i t nh ngha ri p dng bng tr s


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ca cc ha cht tnh . Ttrs tnh c c thkt lun phn ng c xy ra c iu kin chun thc (250C, 1atm) hay khng.

Vi phn ng:

mA + nB -> pC + qD

V d1:

Vi phn ng

NO(k) + 1/2 O2(k) -> NO2(k)

Cch 1: Tnh ca phn ng da vo ca cc cht

[ iu ny ph hp vi thc t, kh NO khng mu tc dng ddng vi O2 ca khng kh

to kh NO2 c mu nu. Khi cho kim loi ng (Cu) vo dung dch HNO3 d m chay long u c to kh mu nu NO2 nu phn ng xy ra trong kh quyn. V tuy vidung dch long c to NO nhng NO tc dng tip vi O2 ca khng kh to NO2.

3.13


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Cch 2: Tnh ca phn ng da vo ca cc cht.

V d2: Tnh ca phn ng

CH2=CH2(k) + H2(k) -> CH3-CH3(k)

Cch 1: Tnh ca phn ng cn cvo trs ca cc cht.


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[ Nhng trong thc tphn ng ny khng xy ra c 25oC, 1atm. Nguyn nhn lvn tc phn ng qu chm iu kin ny nn thc t phn ng nh cha xy ra.

Phi dng cht xc tc thch hp, thc hin phn ng nhit thch hp thc yvn tc phn ng xy ra nhanh hn. Trng hp ny ngi ta ni yu tnhit ng

hc cho php phn ng xy ra nhng yu tng ha hc cha cho php].

Cch 2: Tnh trc ri tnh sau:

III. HA TH(THHA HC)

1. nh ngha ha th

Nhng hthc va nu trn p dng cho nhng htrong lng mi ha cht cahkhng thay i. Trn thc t, qu trnh ha hc km theo s thay i lng ca micht. Nng lng tdo (thng nhit ng p) chng nhng phthuc vo nhit T, psut p m cn ty thuc vo smol ca cc cht c trong h.


44/268

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c gi l ha thca cu ti hay thng nhit ng p mol ring phn ca cuti

hay nng lng tdo mol ring phn ca cu ti ca hn hp.

2. ngha ca ha th

Trong mt hiu kin ng nhit, ng p, nu thm vo hmt lng tht nhsmoldni ca cu ti th thng nhit ng p hay nng lng tdo ca htng ln mt lngl (idni.

Ni chung, ngi ta chrng:

Nhvy, chnh l phn ng gp ring vo nng lng tdo ca hca 1 mol cu ti trng thi hn hp vi cc cu tkhc, thay i vi thnh phn ca hn hp.

Gismt cu ti ca hc hai trsl khc nhau hai trng thi A v B ca htrong iu kin ng nhit v ng p, vi tt csmol ca nhng cu tkhc khng i,

khi mol ca i chuyn tA sang B:

[ Dng du - v c mol i khng cn trng thi A]

Schuyn sxy ra tnhin nu

Vy vt cht chuyn t trng thi c cao n trng thi c thp tng t nhdng

in di chuyn tcc c in thcao n cc c in ththp, do m tha thcgn cho .

ng vmt phn ng ha hc, ha thcn do tim nng ca cu tcho phn ng hahc, v bin i ha hc iu kin ng nhit v ng p xy ra tnhin, i km theo visgim nng lng tdo v ha thth c ng gp vo nng lng tdo.

3.14

3.15


45/268

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3. Biu thc ca ha th

a. Kh l tng nguyn cht

Trong trng hp ny, ha thchnh l nng lng tdo mol ca cu ti nguyn cht.

[ coi (2.39), (2.41) ]

Nu ly bng atm, ta c:

l ha thca cu ti nguyn cht nhit T v p sut lp sut ca i, tnh bng atm.

b. Kh l tng trng thi hn hp

Ngi ta chng minh hthc:

Vi pi l p sut ring phn ca cu ti.

Theo nh lut Dalton, l phn mol ca cu ti v p l p sut ton phn ca h.

(2.49)

Vi:

3.17

3.16

3.18

3.19


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l ha thca cu ti nguyn cht nhit T v p sut p bng p sut ton phnca h.

c. Dung dch

trng thi dung dch long vi cu ti ha tan trong dung mi c nng l Ci, th cthsdng hthc:

l ha thca i ng vi nng bng 1mol/l.

Cc cng thc trong phn cn bng ha hc v dung dch u i tha th.

BI TP CHNG 2 V 3

Cu 1. Cc anh chnghsao vnhng cu sau y:

a). u ng trong tt cmi bin i.

b). u ng trong tt cmi bin i.

Cu 2. Tnh q, ng vi sbc hi ca mt mol toluen 110

o

C dipsut 1atm.

Cho bit: nhit bc hi ca toluen trong iu kin th nghim trn l

nhit si ca toluen l 110oC,

coi hi toluen l kh l tng v ly

C = 12; H = 1

Cu 3. Don du ca (S trong nhng bin i sau y:

3.20


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a) NO(k) + O2(k) -> NO2(k)

b) C2H4(k) + HCl(k) -> C2H5Cl(k)

c) N2(k) + 3H2(k) -> 2NH3(k)

d) CaCO3(r) -> CO2(k) + CaO(r)

e) 2CuO(r) + C(r) -> 2Cu(r) + CO2(k)

f) Ca(r) + O2(k) -> CaO(r)

Cu 4. Mt mol kh l tng gin ng nhit v thun nghch tthtch n

Cu 5. Mt mol kh l tng c mang t trng thi (22,4l; 273 K) n trng thi

(2atm;303 K). Tnh ca bin i trn.

Cu 6. Tnh khi cho mt lng kh argon 25oC, 1atm c thtch 500cm3 gin nn1000 cm3 ng thi t nng n 100oC .

Cu 7. Tnh (S0298 K ca cc phn ng sau:


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a) Ca(r) + O2(k) -> CaO(r)

b) CaCO3(r) -> CaO(r) + CO2(k)

c) NO(k) + O2(k) -> NO2(k)

Cho bit:

Cu 8. a) Tnh cho phn ng:

H2O(k) + CO(k) -> H2(k) + CO2(k)

b) Nu xem cc kh trn nhkh l tng, tnh

c) Bin lun skhthc hin ca phn ng.

Cu 9. Gii thch du ca trong cc bin i sau:

a) H2O(l, - 10oC, 1atm) -> H2O(r, - 10

oC, 1atm)

b) H2O(l, 100oC, 1atm) -> H2O(h, 100

oC, 1atm)

Cu 10. Tnh q, v 1atm. Cho bitnhit bc hi ca , nhit si ca CS2 l 46,2oC.


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Cu 11. Tnh cho bin i:

CH3OH(l, 64oC; 1atm) -> CH3OH (h, 64

oC; 0,5 atm)

Bit rng nhit si ca CH3OH l 64oC v nhit bc hi ca CH3OH 64oC, 1atm l

Coi hi CH3OH nhkh l tng.

Cu 12. Xem phn ng:

CaCO3(r) -> CaO (r) + CO2(k)

a) Tnh bin i

b) Phn ng trn c thc hin c 25oC hay khng?

c) Ti sao phn ng ny c ththc hin c nhit cao?

d) Gis khng i theo nhit , phng tnh nhit thp nht m phn ngc ththc hin c.

e) Kt qutnh c c ph hp vi iu kin thc nghim chto vi sng hay khng?

Cho bit:


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Cu 13. Don du ca trong cc qu trnh sau, c gii thch:

a) O2(k; 25

o

C; 1atm) -> O2(k; 25

o

C; 0,1atm)

b) NH4Cl(r) -> NH3(k) + HCl(k)

c) CO(k) + H2O(h) -> CO2(k) + H2(k)

d) CH4(k) + 2O2(k) -> CO2(k) + 2H2O(h)

e) CH4(k) + 2O2(k) -> CO2(k) + 2H2O(l)

f) N2(k)(25oC; 1atm) -> N2(k)(0oC; 1atm)

g) N2(k)(25oC; 1atm) -> N2(k)(25

oC; 2atm)

h) 2H2(k) + O2(k) -> 2H2O(h)

Cu 14. Don entropi ca cc hsau y stng hay gim khi cc qu trnh vt lxyra iu kin nhit v p sut khng i:

a) Benzen lng ng c thnh benzen rn.

b) Benzen lng bay hi.

c) Pentan, mt cht lng, c ha tan trong hexan, cng l mt cht lng.

Cu 15. Hy chr cht no trong cc cht di y c trsentropi mol chun thc

0298 Kcao hn. Gii thch:

a) Ca(r) v Mg(r)

b) H2O(k) v H2S(k)

c) PCl3(k) v PCl5(k)

d) Cl2(k) v F2(k)


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e) Br2(l) v I2(r)

Cu 16. a) Th hnh (a hnh) l g?

Cc dkin vhai cht th hnh ca phosphor sau:

b) Dng th hnh no bn hn?

c) Dng th hnh no hin din nhiu hn? Gii thch.

Cu 17. Hidrazin, , c dng lm nhin liu cho ha tin. Hidrazin lng c

a) Hidrzin c thiu chtheo phn ng sau y hay khng:

Gii thch.

b) Da vo sliu sau, tnh ton khng nh cu trli trn:

Cu 18. Phn ng ca NO2 vi nc, to acid nitric, gp phn to ma acid.

3NO2(k) + H2O(l) -> 2HNO3(dd) + NO(k)

Tnh ca phn ng ny 25oC. Phn ng c xy ra c iu kin chun

thc hay khng? Cho:


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Cu 19. Cc ng vca Uranium thng c tch ra bng cch dng hin tng r r

(effusion) ca c dng trong l phn ng ht nhn

cng nhchto bom nguyn t. chim

99,28% vsnguyn ttrong tnhin. Hi c vn tc r rln hn hi

ln. Sr rny xy ra tnhin mc d bin i entalpi ca qu

trnh ny gn bng khng. Du ca bin i entropi ca qu trnh ny phi nh

thno?

Cu 20. Ngi ta ni trong mt bin i tnhin lun lun dng v nu bin ithun nghch th =0. iu ny c ng khng?

Ngi ta em 1 mol nc lng v bin n thnh nc mt cch thun nghch 0oC,1atm.

Bit rng nhit phng thch l 1436 cal, tnh .

Cu 21. Trong mt hkhng c lp v gisiu kin l tng c tha.

a) Tnh trong mt bin i ng nhit v thun nghch, gisc sgin tthtch V1n V2.

b) Tnh trong mt bin i ng nhit v bt thun nghch c trng thi u v trng thicui ging nhcu (a)


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c) Tnh trong mt bin i theo mt chu trnh kn.

Cu 22. Phn ng: xy ra vi nhthno?

Da trn , ta c quyn kt lun phn ng khng xy ra c hay khng?

Cu 23. Vphng din nng lng tdo, tm mt hthc tng ng vi cc skinghi sau y:

a) Nc lng si 100oC di p sut 1atm.

b) Ciclohexan dng gh bn hn Ciclohexan dng tu .

c) Vng c nhit nng chy cao hn bc.

Cu 24. Cho bit nhng cu sau y ng hay sai v gii thch:

a) Sgin nkh l tng ng nhit trong chn khng l mt bin i on nhit.

b) Sbin i trn (gin nkh l tng ng nhit trong chn khng) i km vi .

c) Entropi ca kh l tng khng ty thuc vo p sut.

Cu 25. Xem phn ng:

C + O2-> CO2(I)

2C + O2-> 2CO (II)

2Zn + O2-> 2ZnO (III)

1) a) Phn ng no xy ra vi sgim entalpi nhiu nht?


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b) Phn ng no xy ra vi sbin i entropi nhiu nht?

2) a) C thkt lun nhthno vhai phn ng (I), (II) nhit thp?

b) Trli cu hi tng tnhng nhit cao?

c) C thkt lun nhthno vi lc ca C v Zn i vi O2 nhit cao? Suy ra mtp dng quan trng trong knghha hc.

3) a) Tnh bin i entropi khi 1 mol p sut 1atm

cng dng lng. Cho

b) Nhit nng chy , nhit bc hi mol ca H2O l

Tnh (S cho bin i:

H2O(r, 0oC, 1atm) -> H2O(h, 100

oC, 1atm)

Trstrn c xc nh bin i xy ra tnhin (bt thun nghch) hay khng?

Cu 26. Cho phn ng:

Cl2(k) + ClF3(k) -> 3Cl-F(k)

1) Tnh nhit phn ng da trn nng lng lin kt 298 K.

2) Phn ng ny c don nhthno vphng din entropi?

3) Gis ca phn ng khng thay i nhiu theo nhit . Don l thuytxem phn ng c thxy ra 250oC c hay khng?

4) Th nghim cho bit:


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Da trn cc dkin thc nghim, th sinh c thkt lun g vskhthc hin ca phnng trn 250oC?

5) C thkt lun g vnng lng lin kt Cl-F trong ClF v ClF3. Cho bit

EF-F= 38 Kcal.mol-1.

6) Suy ra mt kt lun chung vbng nng lng lin kt cho trong phn gio khoa?

Cu 27. Tnh sthay i ca ha thkhi 1 mol nc bc hi 1 bar v 25oC.

Cu 28. Hy cho bit sthay i ha thca mt kh l tng khi nn ng nhit kh ny

t1,8 atm n 29,5 atm 40oC.


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Chng 4 CN BNG HA HC

Phn ng c gi l phn ng cn bng hay thun nghchkhi n xy ra theo hai chiu ngc nhau trong cng mt iu kin. Do , phn ng cn

bng xy ra khng hon ton, ngha l sau phn ng khng nhng thu c sn phm (C,D) m cn c ccc tc cht (A, B).

V d: Vi phn ng ester ha gia acid acetic vi ru etilic

CH3-COOH + CH3-CH2-OH CH3-COO-CH2-CH3+ H2O

Nu ly 1mol cho tc dng vi 1mol th sau khi phn ng tmc cn bng (coi nhphn ng xong), ta thu c 2/3 mol ester

mol ru

Phn ng cn bng c gi l t trng thi cn bng khitrong cng mt n vthi gian nu c bao nhiu phn ttc cht (A, B) mt i do thamgia phn ng thun to sn phm (C, D) th cng c by nhiu phn ttc cht (A, B)

c to trli tphn ng nghch, lc vn tc phn ng thun v vn tc phn ngnghch bng nhau, lc ny nng cc cht trong phn ng khng thay i na.

Cn bng ha hc c gi l cn bng ng v thc ra lun lun c phn ng thunv nghch xy ra nhng do lng cc cht trong hphn ng khng thay i khi phn ngt trng thi cn bng nn phn ng c coi nhxong. Hn na, c thlm thay itrng thi cn bng ca phn ng bng cch thay i cc yu tnhnng cc cht, nhit, p sut.

I. NH LUT TC DNG KHI LNG

nh lut ny do Gulberg, Waage (Na Uy) a ra nm 1864, nhm xc nh trngthi cn bng ca mt phn ng cn bng.

1. Trng hp cn bng gia cc kh c thxem nhkh l tng

a. Hng scn bng KC


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Xt phn ng cn bng:

Gi ln lt l hng svn tc ca phn ng thun v nghch. Gisphnng thun cng nhphn ng nghch u thuc loi n gin (ngha l phn ng chxy ratrong mt giai on, bc phn ng ring phn ca mi tc cht bng hstlng nguynti gin ng trc mi tc cht trong phn ng).

Vn tc phn ng thun l:

v1= k1[A][B]

Vn tc phn ng nghch l:

v-1= k - 1[C][D]

Gislc bt u phn ng, chc A, B hin din. Vn tc phn ng thun lcu rt ln, vn tc phn ng nghch bng khng. Phn ng cng xy ra lu, nng

cc tc cht A, B cng gim , nng cc sn phm C, D cng tng.

Nhvy, gim dn theo thi gian, cn tng dn theo thi gian. Sau mt thigian vn tc phn ng thun v1 sbng vn tc phn ng nghch , lc ny phn ng ttrng thi cn bng, phn ng c coi nhxong.

v1= v- 1

=> k1[A][B] = k_ 1[C][D]

=>

V l cc hng svn tc phn ng, chty thuc nhit (v ty thuc bn chtca phn ng), cho nn ng vi mt nhit xc nh (v mt phn ng xc nh), ta c:


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cb: cn bng, chnng cc cht C, D, A, B lc t trng thi cn bng.

KCc gi l hng scn bng ca phn ng lin hn nng (mol/l). KCchphthuc nhit v bn cht ca phn ng, m khng phthuc vo nngcc cht trong phn ng.

Hthc trn biu din slin hgia nng ha cht (tc khi lng ca hacht) lc cn bng, chnh l ni dung ca nh lut tc dng khi lng.

C thpht biu nh lut ny nhsau: Khi mt phn ng ng tht trng thicn bng th tstch snng sn phm vi tch snng tc cht l mt hng smt nhit xc nh.

Tng qut vi phn ng:

mA + nB pC + qD

ngi ta chng minh rng, gi trKC:

T khng i l mt hng s, Vi [A], [B], [C], [D] l nng ca A, B, C, D lc cn

bng.

V d: vi phn ng:

2NOCl(k) 2NO(k) + Cl2(k) th hng scn bng KC l:

b. Hng scn bng KP

Hng scn bng ny lin hn p sut ring phn ca ha cht thkh lc cnbng (lc t trng thi cn bng).

[p sut ring phn ca mi cu tca hn hp c thtch chung l V l p sut mcu ty c khi n ng ring mt mnh v cng chim thtch V ca hn hp cngnhit ].


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Xt phn ng:

Gi PA, PB, PC, PDln lt l p sut ring phn ca cc kh A, B, C, D c thxem

nhkh l tng lc cn bng , ln lt l smol ca A, B, C, D hin dintrong thtch V ca hphn ng (bnh phn ng) lc cn bng nhit T (oK).

T ta c:

Thay [A], [B], [C], [D] vo biu thc ca hng scn bng KC:

(4-3)

Do KCchphthuc nhit nn KPcng chphthuc nhit T.

c. Hng scn bng Kx


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Hng scn bng ny lin hn phn smol (phn mol, phn mol) ca cc chttrong phn ng.

[Phn smol (phn mol hay phn mol) x ca cu ti trong hn hp gm nhiu cutl tsgia smol ca i vi tng smol ca cc cu tc trong hn hp.

Xt phn ng:

Gi P l p sut ca hn hp kh lc cn bng; xA, xB, xC, xCln lt l phn smolca A, B, C, D lc cn bng.

Vi l tng smol hn hp gm cc kh A, B, C, D lc cn bng.

Th ca phn ng:


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: Tng hsmol kh sn phm = tng hsmol kh tc cht

Nhvy hng scn bng Kxphthuc vo nhit T v p sut tng qut Pcahn hp kh lc cn bng.

Nu

=> p + q = m + n

=> Tng hsmol kh bn sn phm = Tng hsmol kh bn tc cht

Ch thch:

- Ngi ta chrng trong biu thc ca cc hng scn bng lin hn kh nu trn, takhng ch n cc cht lng v cht rn.

V d:

- Vi phn ng: CaCO3(r) CaO(r) + CO2(k)

Th hng scn bng l Kp= PCO2

- Vi phn ng: NH4Cl(r) HCl(k) + NH3(k)

Th hng scn bng l Kp= PHCl.PNH3

- Vi phn ng: HCl(k) + NH3(k) NH4Cl(r)

Th hng scn bng l Kp=

- Hng scn bng K cng ln, phn ng cng thin vchiu thun, hng scn bng K

cng nhphn ng cng thin vchiu nghch


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- Ty theo hsca phn ng m hng scn bng ca cng mt phn ng c thkhcnhau.

V d:

- Vi phn ng:

- Vi phn ng:

2. Trng hp cn bng trong dung dch lng

Trong trng hp ny, thng hng scn bng KCc p dng cho dung dchlong.

Vi phn ng:

mA(dd) + nB(dd) pC(dd) + pD(dd)

Hng scn bng KCtnh theo cng thc sau:

Vi [C], [D], [A], [B] ln lt l nng ca C, D, A, B trong dung dch lc phn ng ttrng thi cn bng.

Trong trng hp dung dch lng nu trong hphn ng c hin din cht rn th ta khngch n cht rn.

V d:


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Vi , trong dung dch c cn bng vi pha rn AgCl.

3. Slin hgia hng scn bng K vi bin i nng lng tdo ca phn ng

Xt phn ng cn bng ca cc cht thkh:

mA(k) + nB(k) pC(k) + qD(k)

Bin i nng lng tdo G ca phn ng l:

(4-12)

Vi kh c thxem nhkh l tng, iu kin ng nhit, sphthuc ca hmnng lng tdo G theo p sut P l:

Trong l trsnng lng tdo ca 1 mol i 1atm, ng vi nhit T.

(4-13)

Khi phn ng t trng thi cn bng p sut P, nhit T th:


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l bin i nng lng tdo iu kin chun thc (p sut P = 1 atm, nhit T xcnh).

phthuc vo nhit T.

Hthc trn cho bit c thtnh c hng scn bng da vo cc i lng nhitng hc ca ha cht.

Tbiu thc 4-14 cho thy:

- Nu

Do , vi nhng phn ng cn bng tng ng vi rt m c khuynh hng

xy ra gn trn vn, mc cn bng, nng sn phm rt ln.

- Nu

Vy nhng phn ng cn bng ng vi cng dng th cng xy ra khng trnvn, mc cn bng, nng sn phm tng ng rt nh.

Vi trng hp dung dch lng v long vi phn ng:

mA(dd) + nB(dd) pC(dd) + qD(dd)trng thi chun thch hp, ngi ta cng chng minh c hthc:


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Lc phn ng t trng thi cn bng, ta c:

II. NGUYN L CHUYN DCH CN BNG LE CHTELIER

"Khi ht trng thi cn bng, sthay i mt yu tlm ph vcnbng slm

qu trnh chuyn dch theo chiu chng li sthay i y t c trng thi cnbng mi".

Xt mt syu tc thlm thay i mc cn bng:

1. nh hng ca nng

Sthay i nng ca mt cht slm cn bng di i theo chiu chng li sthay i y. Ngha l nu lm tng nng mt cht th cn bng s dch chuyn theochiu lm gim nng ca cht ny xung, tc l chiu cht ny tham gia phn ng; cnnu lm gim nng ca mt cht (nh ly bt cht ny ra khi hphn ng) th cnbng sdch chuyn theo chiu lm tng nng cht ny ln, tc l chiu phn ng to rathm cht ny.

Xt phn ng cn bng:

A + B C + D

Khi phn ng t trng thi cn bng, ta c:

Nu thm cht A vo hphn ng th vn ginguyn trsc

(khng i) th phi tng, nn phn ng cn bng sdi i

theo chiu lm gim A, to ra thm C, D cho n khi no cc nng mi t c trsnhthno cho:


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Tng t, sau khi phn ng t c trng thi cn bng, by ginu ta ly bt Choc D ra khi mi trng phn ng, th cn bng sbph vv cn bng mi scthit lp theo hng to ra thm C, D.

Ni chung mun phn ng cn bng:

A + B C + D

Cho ra nhiu sn phm C, D th ngi ta c th:

- Lm tng nng cc cht tham gia A, B.

- Hay lm gim nng sn phm C, D.

2. nh hng ca p sut

Trong mt phn ng cn bng c lin hn kh, khi lm tng p sut th mc cnbng sdi i theo chiu chng li stng p sut, tc l chiu lm gim smol kh, cnkhi lm gim p sut th mc cn bng sdi i theo chiu lm tng p sut ln, tc lchiu to ra nhiu smol kh hn.

(4-16)

Vi tng shsmol kh sn phm - tng shsmol kh tc cht.

* Nu => smol kh bn sn phm < smol kh bn tc cht.


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phn ng thin vchiu thun (chiu t smol kh hn).

phn ng thin vchiu nghch (chiu to ra nhiu smol kh hn).

V d:

=> ngi ta thc hin phn ng tng hp p sut rt cao khong 200-300atm.

* Nu Smol kh bn sn phm = smol kh bn tc cht.

T:

Sthay i p sut trong trng hp ny khng nh hng n sdi i mc cn bng.

V d:

Sdi i mc cn bng ca phn ng ny khng nh hng bi yu tp sut.


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* Nu Smol kh bn sn phm > smol kh bn tc cht.

T:

* P tng phn ng thin vchiu nghch (chiu t smol khhn).

* P gim phn ng thin vchiu thun (chiu c nhiu smol khhn).

V d:

khi p sut gim, phn ng sthin vchiu to sn phm.

3. nh hng ca nhit

Trong mt phn ng cn bng, khi tng nhit mc cn bng sdi i theo chiuchng li stng nhit tc l chiu lm nhit hxung, chiu thu nhit. Tri li, khihnhit mc cn bng sdi i theo chiu lm nhit tng ln, chiu ta nhit.

V d: vi phn ng:

, nn phn ng ta nhit theo chiu to SO3vy khi hnhit th cn bng sdi i theo chiu to ra thm SO3. Tuy nhin, trnthc t, ta khng thhqu thp nhit v lc by gi, vn tc phn ng squ nh, phnng xy ra rt chm, khng c li vphng din thi gian.

* Cch tnh nhit phn ng ca phn ng cn bng:


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Phn ng ta nhit Phn ng thu nhit

H = Ea1- Ea - 1< 0; H = Ea1- Ea - 1> 0

Gi ln lt l nng lng kch ng ca phn ng thun v phn ng nghch.

iu kin ng p, ta c:

Theo Arrhnius:

k1= A1e-Ea1/RT

k_1= A_1e-Ea-1/RT

Trng hp ny


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Mun xc nh nhit phn ng H ngi ta o hng scn bng K nhiu nhit Tkhc nhau, ri vng biu din lgK theo 1/T , sc mt ng thng m hsgc l

, tung gc l C, t xc nh c H ca phn ng (coi H nhkhng itrong khong nhit T kho st).

Vi gim ngha l khi T tng, ph hp vi skincn bng di i theo chiu thu nhit khi nhit tng.

Vi tng ngha l khi T gim, ph hp vi skincn bng di i theo chiu ta nhit khi nhit gim.

4. p dng nguyn l chuyn dch cn bng


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Ngi ta vn dng nguyn l chuyn dch cn bng ca Le Chtelier iu khinphn ng cn bng thin nhiu vchiu no m ngi ta mun c.

V d: Vi phn ng tng hp amoniac

Phn ng ny ta nhit v c sgim sphn tkh (theo chiu thun). Do mun to rakh nhiu NH3, ngi ta phi:

- Tng nng N2hay H2, lm gim nng NH3

- Tng p sut.

- Hnhit phn ng, tuy nhin khng thhnhit qu thp v nhthvn tc phnng srt chm, nn ngi ta cn chn nhit ti u va thu c nhiu NH3 trongthi gian cng nhanh cng tt.

- Dng cht xc tc thch hp thc y vn tc phn ng xy ra nhanh hn.

Trong thc tiu kin thc hin phn ng tng hp amoniac l:

- Nhit khong 450 - 500oC.

- p sut khong 200 - 300 atm.

- Dng cht xc tc bt Fe c hot ha bng hn hp

Vi mt phn ng cn bng thi im t bt k, bit phn ng ang trng thi cnbng hay ang dch chuyn theo chiu no th ta tnh thng sQ ca phn ng ri so snhvi hng scn bng K tng ng ca phn ng.

Nu Q = K: phn ng trng thi cn bng.

Nu Q < K: phn ng ang dch chuyn theo chiu thun nhm t trng thi cn bng.

Nu Q > K: phn ng ang dch chuyn theo chiu nghch nhm t trng thi cn bng.

mA(k) + nB(k) pC(k) + qD(k)


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BI TP CHNG 4

Cu 1. Cho phn ng cn bng:

Biu thc vn tc ca phn ng thun l:

Hy vit biu thc vn tc ca phn ng nghch.


Biu thc vn tc ca phn ng thun l:

v1= k1[ CO ] [ Cl2 ]3/2

Hy vit biu thc vn tc ca phn ng nghch.



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H2(k) + I2(k) 2HI(k)

763 K c hng scn bng Kc = 45,9 v hng svn tc phn ng thun l

kt= 0,37M- 1.s- 1.

Tm gi trhng svn tc phn ng nghch kn 763 K.

Cu 4. Vi phn ng:

2CH3I(k) -> CH3-CH3(k) + I2(k)

biu thc vn tc phn ng l:

v = k [ CH3-I ]

a) Hy cho bit biu thc vn tc ca phn ng nghch.

b) Tnh gi tr ca phn ng thun 300oC.

c) Phn ng thun c xy ra c 300oC hay khng? Gii thch.

d) nhit no th phn ng nghch xy ra c?

e) Vi qu trnh cn bng:

2CH3I(k) CH3-CH3(k) + I2(k)

Hy cho bit slin hgia .

f) Tnh 300oC.

g) Trong snghin cu vn tc phn ng trn, c cn thit n phn ng nghch 300oC hay khng?

Cho:

Cht CH3I(k) CH3- CH3(k) I2(k)


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(KJ/mol)20,5 - 84,67 62,24

(J/K. mol) 254,6 229,5 260,58

Coi khng i theo nhit .

R = 8,315 J/mol.K.

Cu 5. Vit hng scn bng (nu p sut tnh bng atm).

Chobit hthc lin hgia ca cc phn ng sau:

a) 2NOCl (k) 2NO(k) + Cl2(k)

b) Zn(r) + CO2(k) ZnO(r) + CO(k)

c) MgSO4(r) MgO(r) + SO3(k)

d) 2NO(k) N2(k) + O2(k)

e) CoO(r) + H2(k) Co(r) + H2O(k)

f) NOBr(k) NO(k) + Br2(k)

g) 2SO2(k) + O2(k) 2SO3(k)

h) SO2(k) + O2(k) SO3(k)

i) N2(k) + 3H2(k) 2NH3(k)

j) BaCO3(r) BaO(r) + CO2(k)


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Cu 6. Cho bit nh hng ca p sut trong cc phn ng cn bng sau:

a) 2SO2(k) + O2(k) 2SO3(k)

b) CO(k) + H2O(k) H2(k) + CO2(k)

c) COCl2(k) CO(k) + Cl2(k)

d) N2(k) + 3H2(k) 2NH3(k)

e) 2NO2(k) N2O4(k)

Cu 7. Xem qu trnh:

Cl2(k) 2Cl(k)

Mc cn bng ca qu trnh trn sdi i nhthno khi tng nhit ? Gii thch.

S: Chiu thun.

Cu 8. Xem phn ng:

A(k) B(k) + C(k)

300oC, Kp = 11,5atm

500oC, Kp = 33 atm

a) Phn ng trn thu nhit hay ta nhit?

b) Gisphn ng trn xy ra trong mt giai on th nng lng kch ng Ea ca phnng c trsti thiu bng bao nhiu?

Ly ; phng trnh Van't Hoff cho bit lin hKp theo nhit T l:

Cu 9. 2000 K, phn ng:


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H2(k) + CO2(k) H2O(k) + CO(k)

Tnh nng ca mi ha cht mc cn bng nu mt bnh 10lt cha lc u

.

Cu 10. Snhit phn carbamat amonium c biu din bng phng trnh:

a) 25oC, p sut tng qut ca kh cn bng vi cht rn l 0,116atm. Tnh Kp ca phnng.

b) Giskhi cn bng t c, ngi ta thm vo mt lng kh CO2 c p sut ringphn l 0,1atm. Hi p sut cui cng ca CO2 nhhn hay ln hn 0,1 atm? p sut caNH3 gim hay tng?

Cu 11. Xem phn ng:

COCl2(k) CO(k) + Cl2(k)

a) Trs cho trn c hp l khng?

b) Don phn ng trn thu nhit hay ta nhit?

c) Don nh hng ca nhit n mc cn bng.

d) Tnh .


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e) Tnh hsphn ly l tsgia s

phn t c lc u)

Cu 12. Nng lng tdo mol chun thc ca ln lt l 20,72 v

12,39 .

a) Tnh ca phn ng:

Kt lun.

b) Tnh

Tnh ts . Kt lun.

c) Khi cho acid nitric long tc dng vi kim loi ng ngoi kh tri th nhn thy hintng g? Da vo kt qutrn gii thch.

Cu 13. Cho bit:

Cht CO(k) CO2(k) Pb(r) PbO(r)

298 K(Kcal.mol- 1)

- 26,42 - 94,05 0 - 52,40


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298 K(Kcal.mol- 1)

- 32,81 - 94,26 0 - 45,25

p(cal.K- 1.mol- 1) 6,95 8,76 6,34 11,07

Gistnhit mol ng p khng i trong khong nhit t25oC n 127oC.

a) Tnh ca phn ng:

PbO(r) + CO(k) Pb(r) + CO2(k)

b) Vit biu thc .

c) Tnh

Cho bit phng trnh Van't Hoff lin hgia

Cu 14. a) Cho phn ng:

Tnh p sut tng qut lc cn bng c

b) p sut tng qut 1atm. Tnh Kp.

Nu p sut tng qut gim xung cn 0,5atm, th phn ly bin i nhthno?

Nu thm Argon vo mi trng iu kin ng p (1atm) th phn ly tng haygim?


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Cu 15. Xem cn bng:

CO2(k) + H2(k) CO(k) + H2O(k)

Gis khng thay i bao nhiu vi nhit . Ngi ta cho vo bnh cu phn

ng c thtch .

Tnh:

a)

b) p sut tng qut lc cn bng.

c) Smol ca mi loi ha cht sau khi cn bng t c.

d)

Cu 16. Vit biu thc hng scn bng Kc i vi mi qu trnh cn bng sau:

a) 4NH3(k) + 3O2(k) 2N2(k) + 6H2O (k)


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c) 2SO3(k) 2SO2(k) + O2(k)

f) N2(k) + 3H2(k)


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Chng 5. DUNG DCH

1. Khi nim vdung dch

Ngy nay dung dch khng phi l mt khi nim xa lnhtnh phbin ca n.Tuy nhin hiu ng vdung dch khng phi l chuyn n gin. Vi cc l thuythin i vha hc n nay vn cha gii thch c r rng mt svn vdung dchnh: tnh tan ca cc cht trong dung mi, cc tnh cht ca dung dch c nng cht tanln,... Do vn dtm hiu dung dch khng chxut pht tyu cu vmt thc tin mcn do yu cu vmt l thuyt.

a). Cc hphn tn v dung dch

Dung dch l cc hphn tn nhng khng phi hphn tn no cng l dung dch.Hphn tn l nhng htrong c t nht mt cht phn b(gi l cht phn tn) vomt cht khc( gi l mi trng phn tn) di dng cc ht c kch thc nh. Cc hphn tn c thc phn loi theo trng thi tp hp ca cht phn tn vo mi trngphn tn, hoc theo kch thc ca cc ht trong hphn tn, hoc theo cng tng tcgia cc ht trong hphn tn,...

Ty thuc vo trng thi tp hp ca cht phn tn v mi trng phn tn m ta sc cc hphn tn sau ( K =kh, L = lng, R =rn )

K-K K-L K-R

L- K L-L L-R

R-K R-L R-R

Tuy nhin do tnh cht ca hphn tn phthuc rt ln vo kch thc ca cc htnn sphn loi theo kch thc cc ht l c ngha hn c.

Hphn tn th: kch thc cc ht> cm, do c thnhn thy cc htbngmt thng hoc bng knh hin vi quang hc. Ty thuc trng thi ca cht phn tnm ngi ta phn bit dng huyn ph hay nhtng. Dng huyn ph thu c khi c sphn bht cht rn trong cht lng, v dcc ht t st llng trong nc. Dng nhtng thu c khi c sphn bht cht lng trong cht lng, v dsa l hnhtngin hnh gm cc ht mllng trong cht lng. Cc hphn tn th khng bn v ccht phn tn c kch thc qu ln so vi cc phn t, ion nn ddng lng xung.


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Hphn tn cao hay hkeo: Cc ht phn tn c kch thc trong khong n

, do quan st c cc ht phi dng knh siu hin vi c phng i ln. Vdcho loi hny l gelatine, keo dn, sng m, khi. Cc hkeo cng khng bn v ccht keo dlin hp nhau thnh ht c kch thc ln hn v lng xung. Cc hkeo cnhiu tnh cht rt c bit v c rt nhiu ng dng quan trng trong i sng, do vic

nghin cu hkeo trthnh mt lnh vc nghin cu c lp gi l ha keo.

Dung dch: khi cc ht c kch thc cphn thay ion, ngha l c kch

thc< th hphn tn trthnh ng thv c gi n gin l dung dch. Kchthc v cng b nhca cc ht lm cho chng phn bng u trong mi trng vdn n sng nht vthnh phn, cu to v tnh cht trong ton bthtch ca h,cng nhlm cho hrt bn khng bph hy khi yn theo thi gian. V dkhi ha tanng v mui n vo nc, cc ht ng phn tn di dng phn t, cn cc ht mui

phn tn di dng ion.

Tcc c im nu ta c thnh ngha dung dch nhsau:

Dung dch l hng thgm hai hay nhiu cht m thnh phn ca chng c ththayi trong mt gii hn rng.

nh ngha ny cho thy dung dch ging hp cht vtnh ng nht nhng khc chc thnh phn thay i, trong khi ging hn hp chc chc thnh phn thay

i nhng khc tnh ng nht.

Bng 5.1. Phn loi hphn tn theo kch thc ca tiu phn

H Kch thc tiu phn.n vcm

bn theothi gian

V d

Hphn tn th

-Huyn ph

-Nhtng

>10-5 Khng bn -Ht st llng trong nc.

-Sa

Hkeo 10-5 - 10-7 Khng bn Gelatin

Dung dch


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Trong ho hc chng ta thng lm vic vi cc dung dch lng, do , i vi nhiungi dung dch c hiu l trng thi lng. Thc ra vmt trng thi tp hp, dungdch c thtrng thi kh, lng hoc rn.

Bng 5.2. Cc trng thi tp hp ca dung dch

V d Trng thi ca dungdch

Trng thi ca chttan

Trng thi ca dungmi

Khng kh Kh Kh Kh

Ru trong nc Lng Lng Lng

Thp Rn Rn Rn

Nc ng Lng Rn Lng

Soda Lng Kh Lng

H2tan trong Pd Rn Kh Rn

c). Cht tan v dung mi

Nh trnh by dung dch l hng nht gm cc cht phn tn vo nhau. Chtng vai tr mi trng phn tn, gi l dung mi. Cc cht cn li ng vai tr cht phntn, gi l cht tan. Vi nh ngha ny ta thy ranh gii phn bit gia cht tan v dungmi l khng r rt.

Thng thng dung mi c hiu l cht c trng thi tp hp khng thay i khi

hnh thnh dung dch nu cc cht ban u khc nhau vtrng thi, hoc dung mi l chtchim lng ln khi to thnh dung dch nu cc cht ban u cng trng thi. i khingi ta c thsdng mt tnh cht cthno xc nh dung mi, v d: i vicc hrn-lng, kh-lng th dung mi l cht lng hoc dung mi sl cht kt tinh utin khi lm lnh dung dch.

d). Dung dch long, m c, cha bo ha, qu bo ha, tan

Khi ho tan ng vo nc, ng ng vai tr cht tan, nc ng vai tr dung

mi. Nu lng ng tan trong nc t, ta c dung dch nc ng long. Nu lngng tan trong nc tht nhiu, ta c dung dch nc ng m c. Vy ta c thhiu:

- Dung dch long l dung dch cha mt lng t cht tan.

- Dung dch m c l dung dch cha mt lng ln cht tan.


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Nu tip tc thm ng vo dung dch, ta thy ng tip tc tan ra, dung dch bygischa mt lng ng nhiu hn ban u. Nhng nu tip tc thm ng n mtlc no ta thy ng khng thha tan thm c na mt nhit xc nh, lcny ta c dung dch nc ng bo ha v lc ny lng ng c trong dung dch bngtan ca n. Tng qut ta hiu nhsau:

- Dung dch cha bo ha l dung dch m cht tan c thtip tc tan thm.

- Dung dch bo ha l dung dch m cht tan khng thtan thm c na mt nhit xc nh.

- tan l lng cht tan c vo dung dch to ra mt dung dch bo ha mt nhitxc nh.

Nu nng nhit dung dch ln cao hn, ng stip tc ha tan . Khi lm nguidung dch vnhit ban u t0C th lng ng dso vi tan nhit t0C skttinh tch ra khi dung dch v c shnh thnh tr li dung dch bo ha. Trong mt strng hp, qu trnh kt tinh c thxy ra lp tc hoc sxy ra khi ta thm vo vitinh thca cht tan, hoc lc dung dch. Dung dch cha mt lng cht tan vt qu sovi tan c gi l dung dch qu bo ha, Sir l dung dch nc ng qu bo ham chng ta thng gp.

2. Thnh phn ca dung dch

Do thnh phn ca dung dch c ththay i nn mi quan hvlng ca cc chttrong dung dch phi c xc nh r rng v c nhiu cch khc nhau xc nh miquan h .

a). Nng phn trm khi lng (%)

Sgam cht tan trong 100 gam dung dch.

V d5.1. Dung dch NaOH 20% ngha l c100g dung dch th c 20g NaOH tan trong.

b). Phn mol


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L tlgia smol cht no vi tng smol ca cc cht trong dung dch. i vi

dung dch to thnh thai cht A, B vi smol tng ng l , ta c biu thc phnmol nhsau:

c). Nng molan (m)

Smol ca cht tan c trong 1kg hoc 1000g dung mi.

d). Nng mol

Smol cht tan c trong 1 lt dung dch

V d5.2. Dung dch . Ta c thchn mt loi nng no sdng sao cho tin li vi yu cu nh lng.

V d5.3. Khi trn ln 1,00g etanol vi 100,0g nc ta thu c dung dch c thtch l101ml. Tnh: nng molan. Phn mol ca etanol trong dung dch.

Gii:


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e). Nng ng lng

Mt loi nng khc thng c sdng tnh ton trong cc phng phpphn tch thtch l nng ng lng c nh ngha l sng lng gam ca chttan trong mt lt dung dch. Tnng mol ta c thddng tnh c nng nglng theo biu thc:

l sng lng gam ng vi 1 mol cht tan.

V d5.4. Ta c dung dch ng vi sng lng gam l 2.

Do

Ni chung ta u c ththc hin schuyn i qua li gia cc loi nng , vqua bit c thnh phn ca dung dch.

V d5.5. Dung dch sdng bnh acqui l dung dch H2SO43,75M, c khi lngring l: 1,230 g/ml. Tnh nng %, nng molan v nng ng lng ca H2SO4trong dung dch trn.

Gii:

Khi lng ca 1 lt dung dch: 1000 x 1,230 = 1230g.

Khi lng ca H2SO4trong 1 lt dung dch: 3,75 x 98 = 368g.

Khi lng ca H2O trong 1 lt dung dch: 1230 - 368 = 862g.

Do :


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3. Tng tc gia cht tan v dung mi

a). Nhit ha tan

Khi ha tan NaOH vo nc ta thy dung dch nng ln, ngc li khi ha tan urvo nc th ta li thy dung dch lnh i. iu ny chng tkhi ha tan cht tan vo dungmi khng chn thun xy ra qu trnh khuch tn cc tiu phn cht tan vo cc tiuphn ca dung mi, m cn xy ra qu trnh tng tc gia cc tiu phn vi nhau.

Nhng lc tng tc gia cc tiu phn ca cht tan v dung mi cng chnh l nhng lctng tc quyt nh trng thi tp hp ca cc cht. Chng c bn cht vt l nhlc httnh in, lc Van Der Waals... Hoc bn cht ha hc nhtng tc cho-nhn, lc lin kthydro... Cc lc tng tc thnht gn lin vi cc qu trnh vt l v ch thhin trnnhng khong cch ln hn kch thc phn t. Nhng lc tng tc thhai c thchin trn nhng khong cch gn vi stham gia ca cc obitan nguyn tv phn t.

Skhuch tn cc tiu phn cht tan vo dung mi l nguyn nhn lm cho nng dung dch ng u trong ton bthtch dung dch.

Trong trng hp tng qut cc qu trnh vt l bao gm cc qu trnh ph vmngtinh th, qu trnh khuch tn cht tan vo dung mi,... Gi chung l qu trnh chuyn pha.

Qu trnh ha hc bao gm tt ccc qu trnh tng tc to thnh nhng hpcht c thnh phn thay i gia cht tan v dung mi c gi l ssolvat ha, nu dungmi l nc th c gi l shidrat ha.

Trong a s trng hp cc qu trnh vt l thng tng ng vi qu trnh thu

nhit, cn cc qu trnh ha hc thng ng vi qu trnh ta nhit. Ty cht tan v dungmi, cng nhty nhit v p sut m mt trong hai qu trnh schim u th, kt qudn n l qu trnh ha tan sta nhit hay thu nhit.

Ngi ta nh ngha Lng nhit thu vo hay pht ra khi ha tan mt mol chttan

c gi l nhit ha tan.


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hiu r hn ta xt trng hp ha tan cht rn vo dung mi lng, v dha tanNaCl vo nc, qu trnh c thchia lm 3 bc:

Bc 1 Ph vcu trc tinh thca cht tan to thnh tiu phn ring bit.Qu

trnh ny c trng bng gi tr

Bc 2 Ph vlc lin kt lin phn tgia cc phn tdung mi to ra cckhong trng cho cc tiu phn ca cc cht tan xm nhp. Qu trnh c c trng bng

Bc 3 Xy ra tng tc gia cc tiu phn ca cht tan v cc phn tca dungmito thnh dung dch, tc xy ra qu trnh solvat ha. Qu trnh ny c trng bng gi tr

. chnh l tng ca 3 gi trtrn.

Ty qu trnh no chim u thm gi tr c th(+) hoc (-) hay ni cch khcqu trnh ha tan thu nhit hoc ta nhit.

i vi qu trnh ha tan NaCl trong nc, gi tr phi ln v c du (+) do

phi tn nhiu nng lng bgy lc ht gia cc ion trong tinh th. Gi tr cng rt

ln v c du (-) v xy ra tng tc rt mnh gia cc ion vi cc phn tH2O.

Ty ta c nhit ha tan NaCl trong nc l:

Vmt nhit ng hc, mt qu trnh nu i hi cung cp nng lng cng ln thcng kh xy ra. Qu trnh ha tan NaCl vo nc chi hi mt nng lng tng i

nh, do c thxy ra mt cch tnhin. Gi tr chnh l bin i entalpi ca qutrnh ha tan.

Tuy nhin y cha thgii thch c ti sao NaCl tan tt trong nc. Theonguyn l II ca nhit ng lc hc mt qu trnh xy ra tnhin l mt qu trnh tin n


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mt trng thi xo trn cao hn. Do NaCl tan tt v tuy phi cung cp mt nng lngnhnhng trng thi dung dch t xo trn ln hn rt nhiu so vi ban u, kt qulc shnh thnh dung dch NaCl khi ha tan NaCl vo nc. Cc kt quthu c yhon ton ph hp vi qui lut kinh nghim vtan l .

Bng 5.3. Yu tnng lng ca qu trnh hnh thnh dung dch

tcc cht tan v dung mi khc nhau

Bn cht ca cc cht DH1 DH2 DH3 Kt qu

Dung mi phn cc-chttan phn cc

(+)ln

(+)ln

(-)ln

nh Hnh thnh dung dch

Dung mi phn cc-chttan khng phn cc

(+)nh

(+)ln

(-)nh

(+)ln

Kh hnh thnh dungdch

Dung mi khng phncc-cht tan khng phncc

(+)nh

(+)nh

(-)nh nh

Hnh thnh dung dch

Dung mi khng phncc-cht tan phn cc

(+)ln

(+)nh

(-)nh

ln(+)

Kh hnh thnh dungdch

b). Dung dch l tng

Khi kho st qu trnh ha tan vphng din ng lc hc nh trnh by ngita nhn thy c nhng trng hp m dung dch c hnh thnh vi . l trnghp khi ha tan vo nhau cc cht khng cc v ging nhau vcu trc, lin kt ha hc,v dnhpental v hexan. Trong nhng dung dch nhthlc tng tc ca nhng phntcng loi v khc loi ging nhau. Nhng dung dch nhvy c gi l dung dch ltng. ng lc duy nht a n shnh thnh cc dung dch l tng chnh l sgiatng xo trn, tc gia tng entropy ca dung dch vi cc cht ring lban u. i vidung dch l tng tnh cht ca dung dch khng phthuc vo bn cht ca cht tan mchphthuc vo nng ca chng.

c). nh hng ca cu trc cht tan n tan

Nh cp , m s sphn cc ca mt cht c xc nh bi cu trc ca n, do , gia cu trc v tan cmt mi quan hxc nh. Cc vitamin l nhng v dtiu biu cho thy nh hng cacu trc n tan.


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Ta c thphn vitamin ra lm hai nhm chnh: tan trong du (vitamin A, D, E, K)v tan trong nc (vitamin B, C). Vitamin A c cu to chyu bi C v H, c i lcelectron tng ng nhau nn trong phn tkhng xy ra sphn cc lin kt ng kvdo l cht khng phn cc. iu ny cho thy chng ddng tan trong cc dung mikhng phn cc, v dnhdu m, v khng tan trong cc dung mi phn cc, v dnh

nc.

Hnh 5.1 Cu to ca Vitamin A v Vitamin C

Cc vitamin tan trong du c thhnh thnh v tch trti cc m mtrong cth.Do ta chu ng c mt thi gian di nu trong chn ung thiu ccloi vitamin trn. Ngc li, nu chng qu d c thdn n chng bnh gi ltha vitamin (hypervitaminosis).

i vi cc vitamin tan trong nc, chng ddng bcththi bv do phic bsung thng xuyn. Trc y ngi ta pht hin bnh ph chy mu ca cc thythsng xa t lin do thiu vitamin C, cn bnh ny c chn ng bng cch bsung

y vitamin C.

d). nh hng ca p sut n tan

p sut nh hng khng ng kn tan ca cht rn hoc lng, nhng c tcng ln n tan ca cht kh. Cc loi nc gii kht cha ga khi ng chai phi psut CO2cao nhm bo m t c mt nng ln ca CO2trong dung dch. Khi mnp, do p sut ca CO2trong kh quyn b nn xy ra sthot CO2khi dung dch to nnting bt vc trng.

Sgia tng tan ca kh trong dung dch c thc minh ha trong v dsau: gisang xy ra cn bng gia cht kh v cht lng, ngha l sphn tkh thot ra hoctan vo dung dch vi tc bng nhau. Nu ta lm tng p sut, sphn tkh trong mtn vthtch sgia tng, kh stan vo dung dch vi tc ln hn tc thot ra, lcny nng kh tan trong dung dch stng cho n khi mt cn bng mi c thit lp,v dnhin lc ny dung dch scha mt lng kh tan nhiu hn.


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Mi lin h gia p sut v nng kh tan trong dung dch c th hin quaphng trnh:

P = kC.

Vi P l p sut ring phn ca kh tan trn bmt dung dch.

C l nng ca kh tan trong dung dch

k l hng sc trng ca mi loi dung dch.

y l phng trnh ton hc ca nh lut Henry, n thhin ni dung sau: .

iu quan trng cn phi ch l nh lut Henry chng trong trng hp kh tan

khng phn ng vi dung mi, v d: ng vi trng hp kh O2tan trong nc, nhngkhng ng vi trng hp HCl tan trong nc v y xy ra sphn ly ca HCl.

V d5.6. Mt loi nc gii kht c ng np 250C cha kh CO2vi p sut trn bmt dung dch l 5 atm. Nu p sut ring phn ca CO2trong kh quyn l 4,0.10-4 atm,hy tnh nng CO2trong dung dch trc v sau khi mnp. Hng sHenry ca CO2trong dung dch l 32 l.atm/mol 250C.

Gii:

p dng nh lut Henry ta c:

K = 32 l.atm/mol.

Khi mnp, CO2trong dung dch thot ra v t n trng thi cn bng vi p sut

ca atm, do :


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e). nh hng ca nhit n tan

Vic ha tan cc cht rn vo nc, v dha tan ng hay mui vo nc, m tagp hng ngy c thlm ta i n kt lun rng tan ca cc cht tng theo nhit .Thc skhng phi nhvy. Nhit cao gip qu trnh ha tan xy ra nhanh hn nhng

lng cht tan c thgim i theo nhit .

nh hng ca nhit n tan ca cc mt s cht tan rn trong nc ctrnh by hnh 5.2. Ta thy rng a scc cht c tan tng khi tng nhit , nhngcng c mt scht c tan gim khi tng nhit nh: Na2SO4, Ce2(SO4)3...

Rt kh m tin on sphthuc ca tan ca mt cht theo nhit . Do phng php tt nht l kim tra bng thc nghim.

Hnh 5.2. Sphthuc ca tan ca mt scht rn theo nhit

Hnh 5.3. Sphthuc tan ca cc cht kh khc nhau trong nc theo nhit p sut 1 atm

i vi cht kh th hu nhl tan gim khi tng nhit .


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nh hng ca nhit i vi tan ca cc cht kh c ngha quan trng vmt mi trng. Mt lng ln nc c sdng lm ngui trong cc qui trnh cngnghip, sau khi sdng sbnng ln v c thi trli sng h. Do nng hn nn ncs cha t lng O2 ha tan hn, iu ny lm ph v cn bng hp phO2, lm gimlng O2ha tan trong nc v do vy nh hng n hot ng sng ca cc sinh vt

sng trong nc.

4. Tnh cht ca dung dch khng in ly

Do kt qutng tc xy ra gia cc tiu phn ca cht tan v dung mi, cng nhdo sgim nng cc tiu phn tdo ca dung mi trong qu trnh to thnh dung dchm tnh cht ca cht tan, dung mi thay i v khc vi tnh cht ca dung dch thu c.iu ny c chng minh r rng vi hiu ng nhit, hiu ng thtch, tng nhit si, hnhit ng c ca dung dch so vi dung mi tinh cht.

Khi nng cht tan tng, nh hng ca cc yu tni trn tng mnh lm chotnh cht ca dung dch trnn phc tp hn. Vic nghin cu tnh cht ca cc dung dch rt kh, do , n nay vn cha c l thuyt nh lng i vi nhng dung dch cnng cao.

i vi cc dung dch c nng cht tan nh, c bit nhng nng rt nh,cc nh hng ca nhng yu tni trn c thbqua, do dung dch trthnh gn vil tng, ngha l khng c hiu ng nhit v hiu ng thtch. Trong nhng trng hp

nhvy tnh cht ca dung mi hu nhkhng thay i, cn cc tnh cht ca dung dchth c mt sthay i phthuc bn cht cht tan, v dnhsthay i mu sc, nhng cmt stnh cht khc chphthuc nng cht tan nhp sut hi bo ha, nhit si,nhit ng c, p sut thm thu. Vic nghin cu cc tnh cht ny tng i n ginv xy dng c l thuyt nh lng hon chnh vchng i vi cc dung dch lngv long.

Di y sln lt kho st cc tnh cht .

a). p sut hi ca dung dch

Cc dung dch lng c p sut hi khc ng kso vi dung mi tinh cht. hiuc snh hng ny chng ta xem xt th nghim sau:


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Hnh 5.4. Th nghim kho st nh hng ca cht tan ntnh cht ca dung mi

C hai cc: mt cc ng nc tinh cht v mt cc ng dung dch nc ng,t trong mt chu thy tinh nhhnh 5.4. Sau mt thi gian ta thy thtch ca nc gimcn thtch ca dung dch nc ng tng.

iu ny chc thgii thch c khi p sut hi ca dung mi tinh cht phi lnhn p sut hi ca dung dch cha cht tan khng bay hi, ngha l nu hai bnh c lpnhau th khi cn bng lng hi c thit lp p sut hi to ra trn bmt dung mi tinhcht phi ln hn p sut hi to ra trn bmt dung dch. Do trong mt hkn shahi mnh ca dung mi tinh cht lm cn bng lng hi ca dung dch bdch chuyn theochiu dung dch phi hp thhi lm gim p sut hi trn bmt dung dch. Shpthhi dung mi trn bmt dung dch lm gim p sut hi ca dung mi trong h. t cn bng lng hi trli dung mi tinh cht phi bc hi thm, do cn bng lng hica dung mi tinh cht bdch chuyn theo chiu lm tng p sut hi ca dung mi tinhcht, kt qul xy ra schuyn dung mi tinh cht sang dung dch.

Shin din ca cht tan trong dung dch lm gim sphn tdung mi tdo trongmt n vthtch, do lm gim sphn tdung mi trn bmt v do lm gimkhnng ha hi ca dung mi.

Cc nghin cu vp sut hi ca dung dch lng l tng cha cht tan khng bay hic thc hin bi Francois M.Raoult v c cng thc ha nhsau:


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ng biu din phng trnh ca nh lut Raoult c dng ng thng:y = ax + b.

Vi:

V d5.7. Tnh p sut hi ca dung dch c to thnh bng cch ha tan 158,0g ngSaccaroz (M = 342,3g) trong 643,5cm3 nc 250C, bit 250C khi lng ring canc tinh cht l 0.9971g/cm3v p sut hi ca nc tinh cht l 23,76mmHg.

Gii:

Trong trng hp cht tan bay hi, thng gp i vi cc dung dch lng-lng ltng, phng trnh mrng ca dnh lut Raoult c dng.

Vi:

Cc dung dch l tng nghim ng phng trnh ca nh lut Raoult. Nuphng trnh khng c nghim ng ta c ssai lch. Ssai lch ny c thm hocdng, ngha l p sut hi dung dch c thnhhn hoc ln hn so vi khi tnh tonbng phng trnh Raoult. i vi dung dch cha cht tan khng bay hi thng gp ssai lch nhiu hn so vi dung dch cha cht tan bay hi.

thbiu din sphthuc p sut hi ca dung dch cha cht tan bay hi theophn mol ca dung mi v cht tan c thhin hnh 5.5.


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Hnh 5.5. Sphthuc ca p sut hi ca dung dch cha cht tan bay hi theo

phn mol ca dung mi v cht tan trong trng hp l tng v c xy ra sai lch1: p sut hi dung dch. 2: p sut ring phn ca B. 3: p sut ring phn ca A.

i vi cc dung dch m tng tc gia cht tan- cht tan, dung mi-dung mi,cht tan- dung mi c cng bn cht th tnh cht ca dung dch cng gn vi tnh cht cadung dch l tng. Trong trng hp ny cht tan chlm nhim vpha long dung miv ngc li.

V d 5.8. Dung dch benzen-toluen chng c cng bn cht l khng phn cc.Entanpy ha tan coi nhbng 0, dung dch ny rt gn dung dch l tng v c thxem ldung dch l tng.

Trong mt strng hp dung mi c thc nhng i lc c bit i vi cht tan,v dnhto c lin kt hydro i vi cht tan, lc ny khnng ha hi ca cht tancng nhdung mi trong dung dch u gim v do p sut hi ca dung dch nhhnso vi tnh ton bng phng trnh Raoult, ta c ssai lch m, v d: dung dch acetontrong nc c sai lch m v xy ra lin kt hydro gia aceton v nc.

Ngc li nu tng tc gia cht tan-dung mi yu hn tng tc gia cc phn tca cht tinh cht th khi hnh thnh dung dch nhit ha tan thng c gi tr(+) v cnnng lng lm dn khong cch gia cc phn tcht tan v dung mi khi chng ctrn ln vo nhau. Trong trng hp ny cc phn t cht tan cng nh dung mi ckhuynh hng ha hi mnh hn, ta c dung dch sai lch (+), ngha l p sut hi cadung dch s ln hn so vi gi tr tnh ton bng phng trnh Raoult. V dv trnghp ny l dung dch etanol-hexan. Cc phn tetanol phn cc, cc phn thexan khng


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phn cc, chng tng tc vi nhau rt yu. Entanpy ha tan c gi tr(+)xy ra ssai lchdng.

Bng 5.4. Bng tm tt tnh cht ca cc loi dung dch khc nhau

V d5.9. Mt dung dch c iu chbng cch ha tan 5,81g aceton vo 11,9gCloroform. 350C dung dch c p sut hi l 260mmHg. y l dung dch l tng haykhng? Bit p sut hi ca aceton v cloroform 350C l 345 v 293mmHg.

Gii:

Mun bit dung dch c l tng khng ta tnh p sut hi ca dung dch theophng trnh Raoult ri so snh vi gi trthc nghim.

Theo thc nghim gi tro c l 260mmHg, vy y l dung dch khng l tng.

y c sgim p sut hi ca dung dch nhiu hn dkin tc xy ra ssai lchm. iu ny cho thy gia cht tan v dung mi phi tng tc nhau mnh. Thc vy,gia aceton v cloroform hnh thnh lin kt hydrogen.

ngha ca sgim p sut hi ca dung dch cha cht tan khng bay hi cho tamt phng php thc tin m sphn tv qua gip ta xc nh c phn tlng ca mt cht cha bit. Dng phng trnh Raoult chng ta bit c sphn t


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cht tan hin din, v do chng ta bit khi lng tng ng nn sxc nh cphn tlng.

V d5.10. Mt dung dch c iu chbng cch ha tan 20,0g urea vo 125g nc 250C. p sut hi ca dung dch o c 250C l 22,67mmHg. Xc nh phn t

lngca urea bit p sut hi ca nc tinh cht nhit trn l 23,76mmHg.

Phn tlng ng ca urea l 60,0. Kt quthc nghim ph hp tt vi thc t.

Mt ngha kh

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Bài Giảng Nhiệt Động Hóa Học - Giang Thị Kim Liên, Bài Giảng Động Hoá Học - Phạm Hữu Hùng, Mai Văn Bảy