CHEMISTRY 30 PROBLEMS – HESS’ LAW
1. The heat of combustion of benzene is measured in a bomb calorimeter as -3271 kJ/mol.
Calculate the standard heat of formation of benzene. What is the experimental error?
2. Calculate the DrxnH for the following reaction:
FeO (s) + CO (g) -----> Fe (s) + CO2 (g)
Use the following equations:
3 Fe2O3 (s) + CO (g) -----> Fe3O4 (s) + CO2 (g)
DrH = - 48.26 kJ
Fe2O3 (s) + 3 CO (g) -----> 2 Fe (s) + 3 CO2 (g)
DrH = - 23.44 kJ
Fe3O4 (s) + CO (g) -----> 3 Fe3O4 (s) + CO2 (g)
DrH = + 21.79 kJ
3. Calculate the heat of formation for diborane, B2H6 (g), using the experimental data from
the following calorimetry trials:
4 B (s) + 3 O2 (g) -----> 2 B2O3 (s)
DrH = - 2509.1 kJ
2 H2 (g) + O2 (g) -----> 2 H2O (l)
DrH = - 571.7 kJ
B2H6 (g) + 3 O2 (g) -----> B2O3 (s) + 3 H2O (l)
DrH = - 2147.5 kJ