AP Chem Chap 6
Hess’s Law Practice Problems
Practice problems website: http://chemistry2.csudh.edu/lecture_help/Hesslaw.html
1. Use the thermochemical equations shown below to determine
the enthalpy for the reaction:
C2H6(g) + 7/2 O2(g)  2CO2(g) + 3H2O(l)
C(s) + O2(g)  CO2(g)
H= -196.7KJ
H2(g) + ½ O2(g)  H2O(l)
H= -142.9KJ
2C(s) + 3H2(g)  C2H6(g)
H= -42.3KJ
2. Use the thermochemical equations shown below to determine
the enthalpy for the reaction:
N2O4(g)  N2(g) + 2O2(g)
2NO2(g) N2(g) + 2O2(g)
H=-67.8KJ
N2O4(g) 2NO2(g)
H= 58.2KJ
3. Use the thermochemical equations shown below to determine
the enthalpy for the reaction:
C2H4O(l) + 5/2 O2(g) 2CO2(g) + 2H2O(g)
2C2H6O(l) + O2(g) 2C2H4O(l) + 2H2O(l)
 H= -814KJ
2CO2(g) + 3H2O(l) C2H6O(l) + 3O2(g)
 H= 2742KJ
4. Use the thermochemical equations shown below to determine
the enthalpy for the reaction:
2NO2(g) + 7H2(g)  2NH3(g) + 4H2O(l)
N2(g) + 3H2(g) 2NH3(g)
H=-138KJ
N2(g) + 2O2(g) 2NO2(g)
H=-99KJ
H2O(l) H2(g) + ½ O2(g)
H=-52.5KJ