Advanced Placement (AP) Chemistry Practice Exam

A thermodynamically favored process is indicated by a negative change in free energy, represented as ΔG. This is based on the principles of thermodynamics; when ΔG is negative, it implies that the process occurs spontaneously under the given conditions, meaning the system can move to a more stable state without requiring additional energy input. The Gibbs free energy change (ΔG) is a critical parameter that predicts whether a chemical reaction or process can occur at constant temperature and pressure. In essence, a negative ΔG suggests that the reactants have a higher free energy than the products, and as a result, the process can proceed naturally toward equilibrium. In contrast, a positive ΔH reflects an endothermic process, where energy is absorbed, and does not necessarily indicate favorability. A positive ΔS corresponds to an increase in disorder, which is typically favorable, but it must be considered in conjunction with ΔH when predicting spontaneity through the Gibbs free energy equation (ΔG = ΔH - TΔS). A zero ΔH signifies no heat exchange but does not address the spontaneity of a process on its own. Thus, a negative ΔG is the definitive indicator of a thermodynamically favored process.