Question

Find the heat of reaction (ΔH) for each of the following chemical reactions and note whether each reaction is exothermic or endothermic.
1. H2O(l) -> H2O(g)

This is what I have so far:
H2(g) + ½ O2(g) -> H2O(l) ΔH = -286.0 kJ/mol
H2(g) + ½ O2(g) -> H2O(g) ΔH = -242.0 kJ/mol
H2O(l) -> H2(g) + ½ O2(g) ΔH = +286.0 kJ/mol
1 mol x H2(g) + ½ O2(g) -> H2O(g) ΔH = 1 mol x (-242.0 kJ/mol)
1 mol x H2O(l) -> H2(g) + ½ O2(g) ΔH = 1 mol x (+286.0 kJ/mol)
H2(g) + ½ O2(g) + H2O(l) -> H2O(g) + H2(g) + ½ O2(g) ΔH = 44 kJ
H2O(l) -> H2O(g) ΔH = 44 kJ

Am I on the right track?

Answer 1

Yes but I don't understand why you did all of that work.
dH = (n*dHf products) - (n*dHf reactants)
dH = (1*-242 kJ) - (1*-286 kJ)
dH = -242-(-286) = 44 kJ.
Since dH is +, the reaction is endothermic. I looked up the H^o_f in a set of tables.