The enthalpy of combustion of ethane gas, C2H6(g), is about -1.5*103 kJ/mol.

Question

When ethane reacts with O2(g), the products are carbon dioxide CO2(g) and water H2O(l). How much heat is released during the combustion of ethane gas when 14 mols of O2(g) are consumed. Express your answer in kJ.

Answer 1

2C₂H₆(g) + 7O₂(g) ==> 4CO₂(g) + 6H₂O(l) ... balanced equation

1.5x10³ kJ/mol C₂H₆ x 2 mol C₂H₆ = 3.0x10³ kJ for the combustion

3.0x10³ kJ/7 mol O₂ x 14 mol O₂ = 6x10³ kJ

Looking at this another way:

7 moles O₂ will combust 2 moles C₂H₆

14 moles O₂ will combust 4 moles C₂H₆

4 moles C₂H₆ x 1.5x10³ kJ/mol C₂H₆ = 6x10³ kJ