Acetylene (C2H2) is used in welding torches because it has a high heat of combustion. When 1.00 g of acetylene burns completely in excess O2 gas at constant volume, it releases 48.2 kJ of energy.

Question

Calculate the molar heat of combustion of acetylene (kJ/mol) and the energy kJ) released per mole of O₂ consumed

Answer 1

2C₂H₂ + 5O₂ ==> 4CO₂ + 2H₂O + 48.2 kJ ... balanced equation for complete combustion of acetylene

molar mass C₂H₂ = 26 g/mol

1.00 g C₂H₂ x 1 mol / 26.0 g = 0.0385 moles C₂H₄

moles of O₂ used = 0.0385 moles C₂H₂ x 5 mols O₂ / 2 mols C₂H₂ = 0.0963 moles O₂ used

48.2 kJ / 0.0963 mols O₂ = 501 kJ/mol O₂