4 (c) Dinitrogen oxide is formed when ammonia is oxidised according to the following
equation.
2NH3(g) + 2O2(g) N2O(g) + 3H2O(l)
4 (c) (i) Use the standard enthalpies of formation in the table below to calculate a value for the
standard enthalpy change of this reaction.
............ΔHf / kJ mol–1
NH3(g)= -46
O2(g)= 0
N2O(g) = +82
H2O(l)= -286
This is what i did:
46 x 2= 92
-286 x 3= -858
-858 + 82= -776
ΔH = ΣΔH products – ΣΔH reactants
-776-92= -864
The MS says that the answer is actually -686.
what did i do wrong?