Heats of Formation

H2(g) + O2(g)  H2O(g)   DHf = -242 kJ/mol

H2O(g) H2(g) + O2(g)    DHf = +242 kJ/mol

C(s) + O2(g)  CO2(g)       DHf = -394 kJ/mol

CO2(g)C(s) + O2(g)       DHf = +394 kJ/mol
 
 

Calculate D
Problem 1
2CO(g) + O2(g)2CO2(g)
DH° = -2DHf(CO)  +  2DHf(CO2)
     = -(2 mol)(-111kJ/mol) + (2 mol)(-395kJ/mol) = -568kJ
 

Problem 2
C2H2(g) + H2(g)C2H4(g)
DH° = -DHf(C2H2)  +  DHf(C2H4)
     = -(1 mol)(227kJ/mol) + (1 mol)(52kJ/mol) = -175kJ
 

Problem 3
CH4(g) + 2O2(g)CO2(g)+ 2H2O(g)
DH° = -DHf(CH4)  +  DHf(CO2)  +  2DHf(H2O)
     = -(1 mol)(-75kJ/mol) + (1 mol)(-395kJ/mol) + (2mol)(-242kJ/mol) = -804kJ
 

Problem 4
4NH3(g) + 5O2(g) 4NO(g)+ 6H2O(g)
DH° = -4DHf(NH3) + 4DHf(NO)  +  6DHf(H2O)
      = -(4 mol)(-46kJ/mol) + (4 mol)(+90kJ/mol)  + (6 mol)(-242kJ/mol) = -908kJ

BACK TO MAIN PAGE