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

The Second Law of Thermodynamics states that in any energy exchange, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state; thus, the total entropy of the universe tends to increase over the course of any spontaneous process. Entropy, a measure of disorder or randomness, reflects how energy is dispersed within a system.

During a reaction, if the total entropy of the products is greater than that of the reactants, it indicates a favorable increase in disorder, which is characteristic of spontaneous reactions. This increase in entropy applies to the universe as a whole, incorporating not just the system but also the surroundings. Therefore, the understanding that the entropy of the universe increases during reactions aligns with this thermodynamic principle, leading to the conclusion that the correct answer is that entropy increases.