Why isn't hess's law for calculating the heat of reaction involved in the conversion of diamond to graphite?

Hess's law is applicable when the reactants are different than the products. In a chemical reaction there are rearrangement of atoms such that the chemical property of the reactant is different than that of the product.

Diamond and graphite are purely made up of C atoms with different arrangements of C atoms thus making them allotropes. Hess's law is not applicable for allotropes.

answer; /// i do believe that the correct answer is (c)nuclear bond

answer:

the reaction is type of combination reaction.

explanation:

on the product side, there are 2 molecules of bonded to fe   which means one atom of fe are combined two molecules of . so, balanced chemical equation becomes :

this reaction follows the reaction type of combination reaction. a combination reaction is defined as chemical reaction in which reactants combines together to form a single product.