Question

Consider the combustion reaction,

2C4H2+5O 2--->4 CO2+2H2O
where C2 H2 Hf = 227.4 kJ/mol), CO2 (Hf = –393.5 kJ/mol), and H2 O (Hf = –241.82 kJ/mol). What is the enthalpy of the reaction?

–2,512.4 kJ
–1,256.2 kJ
1,256.2 kJ
2,512.4 kJ

Answer 1

The chemical reaction should be:
2 C₂H₂ + 5 O₂ ---> 4 CO₂ + 2 H₂O
This is complete combustion of a hydrocarbon.
We are also given with
C₂H₂ Hf = 227.4 kJ/mol
CO₂ Hf = –393.5 kJ/mol
H₂O Hf = –241.82 kJ/mol

The enthalpy of the reaction is
4(-393.5) + 2(-241.82) - 2(227.4) = -2512.44 kJ/mol