Medical College Admission Test (MCAT) General Chemistry Practice Exam 2026 - Free MCAT Chemistry Practice Questions and Study Guide

In a chemical reaction, the entropy change for the forward reaction is indeed equivalent to the negative of the entropy change for the reverse reaction. This relationship stems from the principles of thermodynamics, specifically the second law, which states that the total entropy of an isolated system can only increase over time.

When a reaction proceeds in the forward direction, it may increase or decrease the entropy of the system depending on the nature of the reactants and products. For instance, if the products have greater disorder than the reactants, the forward reaction will have a positive entropy change, indicating an increase in entropy. Conversely, when that same reaction proceeds in the reverse direction, it will demonstrate an entropy change that reflects a decrease in disorder, which is the negative of the forward entropy change.

This concept underscores the fact that the same transformation can be viewed from two perspectives: the forward process, which results in a specific entropy change, and the reverse process, which must inherently reflect the opposite change in entropy. Thus, if the forward reaction has a certain positive or negative entropy change, the reverse reaction will have the same magnitude of entropy change but of the opposite sign. The answer provided accurately captures this fundamental relationship in thermodynamics.