2025 MCAT General Chemistry Practice Exam – Your Comprehensive All-in-One Study Guide for Success!

The direction of a reaction during a phase change is primarily dictated by temperature because temperature influences the energy levels of the molecules involved. As temperature changes, the kinetic energy of the particles also changes, affecting how they interact.

For instance, when the temperature increases, molecules gain kinetic energy, which can facilitate a transition from a solid to a liquid or from a liquid to a gas, as the increased energy helps overcome the intermolecular forces holding the molecules in a more ordered state. Conversely, decreasing the temperature typically favors phase changes that result in a more ordered state, such as from a gas to a liquid or from a liquid to a solid, as the energy decreases and the forces become more significant.

While pressure, volume, and specific heat can impact phase changes, particularly in systems like gases, it is temperature that fundamentally drives the process based on kinetic theory. High temperatures encourage phase transitions to less ordered states (e.g., gas), whereas low temperatures promote more ordered states (e.g., solid).