What is the heat of combustion of ethane, C 2 H 6 , in kilojoules per mole of ethane? Enthalpy of formation values can be found in this list of thermodynamic properties.

Answer 1

2C₂H₆ + 7O₂ ==> 4CO₂ + 6H₂O ... balanced equation

The heat of combustion for this reaction will be equal to the sum of the enthalpy of formation of the products - the sum of the enthalpy of formation of the reactants. Or...

∆H_rxn = ∑∆H_products - ∑∆H_reactants

Look up ∆H_formation CO₂ and multiply it by 4 and add that to 6x the ∆H for H₂O

From that value subtract 2x the ∆H_formation for ethane and that will give you the answer

NOTE: the ∆H_formation for O₂ is zero so doesn't need to be included in the equation