Arkansas State University Department of Chemistry and Physics

1. Calculate the DH^o_rxn from the DH^o_f  for the following reaction:

a)    PbO _(s)   +   CO _(g)     ------->    Pb _(s)     +  CO_{2 (g)}         DH^o_rxn = -65.7 kJ

b)   SiH_{4 (g)}   +  2 O_{2 (g)}    ------->    SiO_{2 (s)}   +  2 H₂O _(l)     DH^o_rxn = -1516.8 kJ

c) 2 FeS_{2 (s)}  +  5.5 O_{2 (g)}    ------->  Fe₂O_{3 (s)}  +  4 SO_{2 (g)}   DH^o_rxn = -1656.4 kJ
 

2. Determine the DH_rxn  using Hess' Law

a)  Determine the enthalpy of formation for MnO_{2 (s)}

        Mn _(s)  +   O_{2 (g)}   -------->   MnO_{2 (s)}

Given:

4 Al _(s)   +  3 O_{2 (g)}  ------->  2 Al₂O_{3 (s)}                                  DH_rxn  = -3352 kJ/mol
 

4 Al _(s)  +   3 MnO_{2 (s)}  ------->    3 Mn _(s)   +   2 Al₂O_{3 (s)}       DH_rxn = -1937 kJ/mol

DH_f = -471.7 kJ/mol
 

b)  Determine the heat of hydrogenation for

        C₃H_{4 (g)}  +  2 H_{2 (g)}   -------->   C₃H_{8 (g)}

Given:

2 H_{2 (g)}   +   O_{2 (g)}  ------->  2 H₂O _(l)                                      DH_rxn  = -571.6 kJ/mol
 

C₃H_{4 (g)}  +   4 O_{2 (g)}  ------->    3 CO_{2 (g)}   +   2 H₂O _(l)          DH_rxn = -1937 kJ/mol
 

C₃H_{8 (g)}  +   5 O_{2 (g)}  ------->    3 CO_{2 (g)}   +   4 H₂O _(l)          DH_rxn = -2220 kJ/mol

DH_rxn = -288.6 kJ/mol