Advanced Placement (AP) Biology Practice Exam

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to occur. However, they do not alter the overall change in free energy (∆G) of the reaction. The free energy change is a thermodynamic property that reflects the difference in energy between the reactants and the products, indicating whether a reaction is spontaneous or requires energy input.

Since enzymes facilitate the transition state and increase the rate of reaching equilibrium without affecting the energy levels of the reactants and products, the free energy change remains unchanged. Thus, the correct understanding is that enzymes do not alter the overall change in free energy; they simply allow the reaction to occur more quickly under otherwise unchanged conditions.