Thermodynamics

Enthalpy of combustion, is the heat energy that is absorbed or released when one mole of a substance undergoes complete combustion in the presence of excess oxygen under the standard conditions.

Given 2C+2H→C₂H4 (g) △H₁ = 52KJ mol^-1

C+O₂→ CO₂ (g) △H₂ = -394 KJ mol^-1

H₂ + O₂ → H₂O (g) △H₃ = -286 KJ mol^-1

For Combustion of C₂H₄

C₂H₄ + 3O₂ → 2CO₂ +2H₂O

For △ H → 2 [△H₂+△H₁] - [△H₁]

= 2 [-394+(-286)]- 52

= -1360 - 52

= -1412 KJ mol^-1