Chem 1010 Tutorials
Tutorial 10B – Enthalpies of Formation
Fall 2013
1.
What is vapH for the vaporization of iron if fH of Fe(l) is 12.40 kJ∙mol and fH Fe(g) is 415.5 kJ∙mol .
The vaporization process can be represented by the following chemical equation:
Fe(l) → Fe(g)
2.
What is the conH of condensation for hydrazine, N2H4, if fH of N2H4(l) is 50.63 kJ∙mol and fH of
–1
N2H4(g) is 95.35 kJ∙mol . The condensation process can be represented by the following equation:
N2H4(g) → N2H4(l)
3.
What is the vapH of vaporization for dinitrogen tetraoxide if fH of N2O4(l) is -19.56 kJ∙mol and fH of
–1
N2O4(g) is 9.079 kJ∙mol . The vaporization process may be represented by the following equation:
N2O4(l) → N2O4(g)
4.
Consider the combustion of ethanol:
C2H5OH(l) + 3 O2(g) → 3 H2O(l) + 2 CO2(g)
o
o
Calculate rH for the combustion of ethanol (for the equation as written), if fH of CO2(g) is
–1
o
–1
o
–1
–393.5 kJ∙mol , fH H2O(l) is –285.8 kJ∙mol and fH for ethanol is –277.7 kJ∙mol .
5.
Consider the combustion of ethane:
2 C2H6(g) + 7 O2(g) → 6 H2O(l) + 4 CO2(g)
o
–1
–1
–1
If fH of CO2(g), H2O(l), and C2H6(g) are –393.5 kJ∙mol , –285.8 kJ∙mol , and –84.68 kJ∙mol respectively,
o
what is the rH for the reaction as written?
6.
(a)
(b)
Write the formation equations for NaHSO4(s) and (NH4)2Zn(CrO4)2(s).
Consider the combustion of butane:
2 C4H10(g) + 13 O2(g) → 10 H2O(l) + 8 CO2(g)
o
o
–1
o
Calculate rH for the reaction as written if fH of CO2(g) is –393.5 kJ∙mol , fH of H2O(l) is –
–1
o
–1
285.8 kJ∙mol , and fH of C4H10 is –125.7 kJ∙mol .
7.
(a)
(b)
Write formation equations for KHSO4(s) and (NH4)2Cr2O7(s).
Consider the thermochemical equation for the combustion of glucose:
o
–1
C6H12O6(s) + 6 O2(g) → 6 H2O(l) + 6 CO2(g)
rH = –2816 kJ∙mol
o
–1
o
–1
If fH of CO2(g) is –393.5 kJ∙mol and fH of H2O(l) is –285.8 kJ∙mol calculate the enthalpy of
formation of glucose.
8.
(a)
(b)
Write formation equations for NaBH4(s) and Ag(NH3)2Cl(s).
Given:
2 C6H6(l) + 15 O2(g) → 6 H2O(l) + 12 CO2(g)
o
–1
–1
–1
If fH of CO2(g), H2O(l), and C6H6(l) are –393.5 kJ∙mol , –285.8 kJ∙mol and 49.0 kJ∙mol
o
respectively, what is rH for the reaction as written?
9.
(a)
(b)
Write formation equations for Na3Co(CN)5I(s) and BrF5(l).
Consider the combustion of toluene:
o
–1
C7H8(l) + 9 O2(g) → 4 H2O(l) + 7 CO2(g)
rH = –3910 kJ∙mol
Using this thermochemical equation and information from appendix II of your textbook (Tro),
calculate the molar enthalpy of formation of toluene.
o
o
o
o
–1
o
o
–1
–1
o
o
–1
o
Answers:
1. vapHo = 403.1 kJ∙mol–1 Fe
2. conHo = –44.72 kJ∙mol–1 N2H4
3. vapHo = 28.64 kJ∙mol–1
4. rHo = –1366.7 kJ∙mol–1
5. rHo = –3119.4 kJ∙mol–1
6. b) rHo = –5754.6 kJ∙mol–1
7. b) fHo = –1260. kJ∙mol–1
8. b) rHo = –6534.8 kJ∙mol–1
9. b) fHo = 12 kJ∙mol–1