Question

Consider the reaction: 2clf3(g) + 2nh3(g) → n2(g) + 6hf(g) + cl2(g) when calculating the δh°rxn, why is the δhf° for n2 not important?

Answer 1

Actually, the heat of reaction hrxn s calculated by taking the sum of the heats of formation of the products minus the sum of the heats of formation of the reactants. However, at heat of formations of pure elements at atmospheric conditions is zero, therefore the hf of N2 is not important since it is zero anyway.