Unit 4
Thermochemistry
AP Chemistry Problem Set
SC 4-4: Enthalpy of Formation
20. Write an equation to represent a reaction that provides the heat of formation of carbon
dioxide (CO2)?
21. Write an equation to represent a reaction that provides the heat of formation of CH3Cl?
22. Write an equation to represent a reaction that provides the heat of formation of Fe3O4?
23. Calculate the heat of reaction (kJ) using the listed heats of formation:
CH4(g) + 4 F2(g) CF4(g) + 4 HF(g)
Hof CH4 = -74.81 kJ/mole
Hof CF4 = -925.0 kJ/mole
Hof HF = -271.1 kJ/mole
Unit 4
Thermochemistry
AP Chemistry Problem Set
24. Use the given standard enthalpies of formation to determine the heat of reaction of the
following reaction:
2 Na(s) + 2 H2O(l) 2 NaOH(s) + H2(g)
Hof NaOH(s) = -426.8 kJ/mole
Hof H2O(l) = -285.8 kJ/mole
25. Calculate Hof (kJ) for the following reaction from the listed standard enthalpies of
formation:
P4O10(s) + 6 H2O(l) 4 H3PO4(aq)
Hof P4O10(s) = -2984.0 kJ
Hof H2O(l) =
Hof
-285.8 kJ
H3PO4(aq) = -1277.4 kJ
Unit 4
Thermochemistry
AP Chemistry Problem Set
26. The standard enthalpy of formation of propene, C3H6, is +20.6 kJ/mole. Calculate the heat
of combustion of one mole of C3H6. The heats of formation of CO2(g) and H2O(l) are -394
kJ/mole and -285.8 kJ/mole respectively.
27. Using the following information calculate the heat of formation of N 2H4.
N2H4(l) + O2(g) N2(g) + 2 H2O(l)
Ho = -622.4 kJ
Hof H2O(l) = -285.9 kJ/mole
Unit 4
Thermochemistry
AP Chemistry Problem Set
28. Using the given standard enthalpies of formation and the heat of reaction, calculate the
heat of formation of C2H2(g).
CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g)
Ho = -127.2 kJ
Hof Ca(OH)2(s) = -986.2 kJ/mole
Hof CaC2(s) = -60.6 kJ/mole
Hof H2O(l) = -285.85 kJ/mole
29. The heats of formation of CO2(g) and H2O(l) are -394 kJ/mole and -285.8 kJ/mole
respectively. Using the data for the following combustion reaction, calculate the heat of
formation of C2H2(g).
2 C2H2(g) + 5 O2(g)
4 CO2(g) + 2 H2O(l)
Ho = -2601 kJ