Calcualte the standard enthaslpy change, ?H ^{o ,} for the combustioni of ammonia, NH ₃ (g), to give nitric oxide, NO (g), and water, H ₂ O (I). The enthalpies of formation, ?H ^o _f , are -68.32 kcal /mole for H ₂ O (I), -11.2 kcal / mole for NH ₃ (g), and 21.57 kcal / mole for NO (g).

4 NH ₃ (g) + 50 ₂ (g) ® 4 NO (g) + 6H ₂ O (I)