<span>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.</span>
The key difference between empirical and molecular formulas is that an empirical formula only gives the simplest ratio of atom whereas a molecular formula gives the exact number of each atom in a molecule.
