What occurs to the energy of the system during molecular collisions?

In the context of molecular collisions in a gas, the correct understanding is that the average kinetic energy of the molecules remains constant provided that the temperature of the system remains unchanged and that no external work is done on or by the gas. This is a fundamental aspect of the kinetic molecular theory, which posits that gas molecules are in constant random motion, and energy is transferred between colliding molecules during these interactions but not lost or gained overall.

When two gas molecules collide, they exchange energy during the collision. If one molecule is moving faster (has higher kinetic energy), it may transfer some of that energy to the slower-moving molecule. However, in a closed system at equilibrium and constant temperature, these energy transfers average out over many collisions, resulting in no net change in the internal energy of the system. Thus, the energy remains the same when viewed from a macroscopic perspective, affirming that the average kinetic energy is a function solely of the temperature of the gas.