How does thermal energy affect the motion of particles in a liquid?

Thermal energy is fundamentally linked to the motion of particles in a liquid. According to the kinetic molecular theory, matter consists of particles in constant motion, and this motion is a direct manifestation of thermal energy; specifically, the greater the thermal energy of a particle, the faster it moves.1

The effects of thermal energy on particle motion and liquid behavior include:

• Increased Mobility: As thermal energy increases, the particles move more rapidly. This enhanced mobility allows liquids to flow more easily, which is observed as a decrease in viscosity upon heating.21
• Phase Transitions: Heating a solid provides the necessary energy for particles to overcome their fixed positions and move about in the liquid state. Further increases in thermal energy provide the heat of evaporation, enabling particles to escape the liquid's cohesive forces entirely and enter the gaseous state.34
• Mixing and Solubility: In mixtures of polar and nonpolar substances, thermal energy can offset the cohesion between identical molecules, allowing the liquids to mix in proportions that would not occur at lower temperatures.5