How much energy must be added to 2 mol h2o(g) to cause it to decompose into h2 and o2?

The forward reaction is:
2H₂(g) + O₂(g) → 2H₂O(g); ΔH = -484 kJ

The forward reaction releases 484 kilojoules of energy to form water. As per the reaction equation, in order to cause two moles of water to decompose and make the reaction proceed backwards, 484 kilojoules of energy must be added to water.