7/28/2019 Jr Chemistry - Page 22
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Jr.Inter Chemistry 22
6. Is increase of entropy the criterion for spontaneity ? Why
?
Ans : Change in entropy ( )" S = positive' is a condition but is
not necessary and sufficient
condition for the spontaneous nature of a reaction.
7. The equilibrium constant for a reaction is 10. What will be
value of G
?
1 1
8.314 , 300R JK mol T K
= = .
Ans : Formulae 0 lnG RT k =
= -2.303 RT log K ,= -2.303 8.314 300 log 10 =
-5774.14J/mole
k = 10,R = 8.314 J/K. mole ,T = 300 K
8. State the third law of thermodynamics.
Ans : State the third law of thermodynamics : "The entropy of a
pure and perfectly crystalline
substance is zero at the absolute zero of a temperature ( )0273
C "
lim 0 0TS =
This law imposes a limitation on the value of entropy.
0
.
T
P
TS
CdT
T=
9. State the second law of thermodynamics and explain it.
Ans : II law of thermodynamics :
Statements :
i) It is impossible for a self acting machine unaided by any
external agency to convert
heat from a body at low temperature to a body at higher
temperature"
ii) " All spontaneous processes are thermodynamically
irreversible and entropy of the
system increases in all spontaneous processes."
iii) "For any spontaneous process taking place in an isolated
system, the change in entropy
( )S is positive."
10. Calculate the entropy change in surroundings when 1.00 mole
of H2O
(1)is formed under standard
conditions 1fH 74kJ mol
= = = =
A. qrev
= ( H ) e =286 kJ mol1=286000Jmol1
(surrounding)S =1
revq (286000Jmol )
T 298K
=
= 959 J K1 mol1.
11. The equilibrium constant for a reaction is 10. What will be
the value of G
