The standard molar entropy of a substance is the absolute entropy of 1 mole of the substance in the standard state. For any chemical reaction, the standard entropy change is the sum of the standard molar entropies of the products minus the sum of the standard molar entropies of the reactants.

Entropy change (∆S) is the change in the disorder (entropy) within a system as the result of a chemical or physical process. Like entropy, it is also measured in J K^-1 mol^-1. Certain types of reactions are accompanied by specific entropy changes.

Subtract the sum of the absolute entropies of the reactants from the sum of the absolute entropies of the products, each multiplied by their appropriate stoichiometric coefficients, to obtain ΔS° for the reaction.

When there is a phase transition, the system releases or absorbs a large amount of energy per volume change. Hence, when there is an increase in heat and temperature, it increases the disorder of the molecules and increases the entropy.