Spontaneous Reactions and Gibbs Free Energy

Changes are thermodynamically feasible if the total entropy change is positive, so for an endothermic reaction, if an increase in entropy is more significant than the endothermic nature of the reaction will be spontaneous. For example when pure ethanoic acid is added to solid ammonium carbonate a violent reaction takes place.2CH₃COOH(l) + (NH₄)₂CO₃(s) → 2CH₃COONH₄(s) + H₂O (l) + CO₂(g)The reaction is endothermic, but there is an increase in the total entropy, ΔS_total is positive so the reaction is thermodynamically spontaneous.The free energy measured at constant pressure is called the Gibbs Free EnergyΔG^θ = ΔH^θ - TΔS^θwhere T is in Kelvin and ΔS^θ is the entropy change of the system. ΔG is a measure of the chemical potential of a system. For a reaction to be spontaneous ΔG must be negative.