In order to determine the energy changes involved, we require the reaction. The reaction under consideration in this question is 2H₂ + O₂ → 2H₂O, ΔH = -484 kJ/mol
We see that if 2 moles of hydrogen react, 484 kJ of energy are released. We may use a ratio to determine the amount of energy released when 1.8 moles of hydrogen react:
2 : 484 1.8 : x
x = 435.6
435.6 kilojoules of energy are released when 1.8 moles of hydrogen react.
