Phase changes in a reaction significantly influence the overall entropy change by either increasing or decreasing the system’s disorder.

Entropy is defined as a measure of the disorder or randomness within a system. In the context of a chemical reaction, the entropy change, denoted as $\Delta S$, is the difference in entropy between the products and the reactants. When a phase change occurs during a reaction, it can greatly impact the overall entropy change due to the varying levels of disorder associated with different phases of matter. Specifically, gases exhibit greater disorder compared to liquids, while liquids are more disordered than solids. Consequently, if a reaction involves a phase change from a solid to a liquid or from a liquid to a gas, the entropy of the system will increase. Conversely, if the phase change occurs from a gas to a liquid or from a liquid to a solid, the entropy will decrease.

Additionally, the entropy change in a reaction is affected by the number of particles involved. If a reaction produces a greater number of particles, the entropy will increase due to the increased number of possible arrangements of those particles, leading to heightened disorder. On the other hand, if the reaction results in fewer particles, the entropy will decrease.

Temperature also plays a crucial role in influencing the entropy change during a phase change. At elevated temperatures, particles possess more kinetic energy and move more freely, which contributes to greater disorder and higher entropy. In contrast, at lower temperatures, particles have reduced kinetic energy and move less freely, resulting in lower entropy.

In summary, phase changes in a reaction can significantly impact the overall entropy change. The direction and magnitude of this change depend on the nature of the phase transition (from more ordered to less ordered or vice versa), the number of particles produced, and the temperature at which the phase change occurs. Understanding these factors is essential for predicting the spontaneity of a reaction, as reactions tend to proceed in the direction that maximizes the disorder of the system, thereby increasing the entropy.