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) = -285.8 kJ

Hof 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 N2H4.

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