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PlanningEnergetics
Standard enthalpy change of neutralisation0 Definition0 Dependent variable0 Independent variable0 Value of Hneut
o
0 Basicity of acids
Typical Experimental Set-up
For each set of data
Amt. of HCl
Amt. of NaOH
Initial temp. of HCl
Initial temp.of NaOH
Ave. initial temp.
Typical Table of Data
Amt. HnX Amt. NaOH
Max. temp.
T = Tmax - Tinitial
50 1040 2030 3020 4010 50
For example, using 1 mol dm-3 acid and NaOH
HnX + nNaOH NanX + nH2O
Better than the word “Final”
Typical Graph – type 1
Vol. of NaOH used / cm3
10 2030
40 50
If Basicity of acid, n = 1
Amt. HnX Amt. NaOH
Max. temp.
T = Tmax - Tinitial
50 1040 2030 3020 4010 50
Work out using HClAmt. HCl Amt.
NaOHHneut
o
50 10 - 60 x c x T1
0.0140 20 - 60 x c x T2
0.0230 30 - 60 x c x T3
0.0320 40 - 60 x c x T2
0.0210 50 - 60 x c x T1
0.01
Typical Graph – type 2
Vol. of NaOH used / cm3
10 2030
40 50
Type 1
Type 2
If Basicity of acid, n = 2
Amt. HnX Amt. NaOH
Max. temp.
T = Tmax - Tinitial
50 1040 2030 3020 4010 50
Work out using H2SO4
Amt. H2SO4
Amt. NaOH
Hneuto
50 10 - 60 x c x T1
0.0140 20 - 60 x c x T2
0.0230 30 - 60 x c x T3
0.0320 40 - 60 x c x T4
0.0410 50 - 60 x c x T2
0.02
Most informative region
Vol. of NaOH used / cm3
10 2030
40 50
Type 1
Type 2
Monobasic
Dibasic
Considerations for accuracy and
reliability0 Insulation – styrofoam cup, lid0 Stability of set-up – beaker0 thermometer – precision0 Consistency of stirring
Standard enthalpy change of combustion
0 Definition0 Dependent variable0 Independent variable
Typical Experimental Set-up
Typical Table of Data
For example,CnH2n+2O + O2 nCO2 + (n+1)H2O
Initial mass of spirit
lamp
Final mass of spirit
lamp
Initial temp
Max. temp.
Raw Data
Work out using C2H5OH
Mass of C2H5OH
T Hcombustiomo
- mH2O x c x TnC2H5OH
Processed Data
Refer to HCI/2010 for consideration on heat absorbed by Cu can.
Considerations for accuracy and
reliability0 Heat loss to surroundings –
insulation of Cu can0 Heat loss to Cu can – consider
heat capacity of Cu can0 Incomplete combustion of alcohol
If diff alcohols are used
Standard enthalpy change of reaction
0 Definition0 Dependent variable0 Independent variable
Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g)
Suitable quantities of reactants to use: 0.010 mol Na2CO3 (1.06 g Na2CO3)
0.020 mol HCl ( 20 cm3 1 mol dm-3 HCl)
Mass of empty weighing bottle =
Mass of weighing bottle and Na2CO3=
Mass of emptied weighing bottle and residue
=
Volume of HCl used =
Initial temp of HCl =
Typical Experimental Set-up
Table of dataTime / min Temperature /
oC012
3.54567
Typical graph
Temp / oC
Time / min1 23.5
4 5 6 7
23.5
Temp / oC
Time / min
T
At 3 min, time of addition of Na2CO3
Calculate Hreactiono
Hreactiono = - MHCl x c x T
nNa2CO3
Assume density of HCl = 1 g cm-3
Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g)
NaHCO3(s) + HCl(aq) NaCl(aq) + CO2(g) + H2O(l)
T
Calculate Hreactiono
Hreactiono = + MHCl x c x T
nNaHCO3
Assume density of HCl = 1 g cm-3
NaHCO3(s) + HCl(aq) NaCl(aq) + H2O(l) + CO2(g)
Think about…
0 The standard enthalpy change of:
Na2CO3(s) + HCl(aq) NaHCO3(aq) + NaCl(aq)