Calculating Entropy Changes

If we know the absolute standard molar entropies, S^o, of the reactants and products of a reaction we can calculate the entropy change of the reaction using the following equation, which is similar to the shorthand version of Hess's law:

Many handbooks and textbooks have tables of absolute standard molar entropies.

Note: As an approximation, introductory courses assume that entropy changes do not change with temperature.