Write down the equation for the Gibbs Free Energy change of a reaction. Hence explain why, for a spontaneous endothermic reaction, there must be an increase in the total entropy.

Gibbs Free Energy change: (delta)G = (delta)H - T(delta)S For a spontaneous chemical reaction, (delta)G must be negative. An endothermic reaction has a positive (delta)H value therefore, in order for the reaction to be spontaneous, the T(delta)S term must be positive. Since T is in units of K, it cannot be negative, hence (delta)S can only be positive to have an overall positive T(delta)S term. Since (delta)S is positive, this implies an increase in entropy therefore the entropy must increase for the reaction to be spontaneous.