Graphs of Gibbs free energy
Whether a reaction is product-favored, that is, whether the reactants are converted to products under standard-state conditions, is reflected in the sign of its Δ r G° . This equation Δ r G° = Δ r H° − T Δ r S° shows that the sign of Δ r G° depends on the signs of Δ r H° and Δ r S° , and, in some cases, the absolute temperature (which can only have positive values). Four possibilities exist: Both Δ r H° and Δ r S° are positive —an endothermic process with an increase in system entropy. Δ r G° is negative if T Δ r S° > Δ r H° , and positive if T Δ r S° < Δ r H° . Such a process is product-favored at high temperatures and reactant-favored at low temperatures. Both Δ r H° and Δ r S° are negative —an exothermic process with a decrease in system entropy. Δ r G° is negative if | T Δ r S °| < |Δ r H °| and positive if | T Δ r S °| > |Δ r H °|. Such a process is product-favored at low te...
