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

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