What happens to the entropy of a system during an irreversible process?

During an irreversible process, the entropy of a system increases. This is a fundamental principle of thermodynamics, specifically in the second law, which states that in any natural thermodynamic process, the total entropy of an isolated system can never decrease over time.

Entropy is a measure of the number of ways a system can be arranged, or the amount of disorder within the system. When an irreversible process occurs—such as mixing two gases, spontaneous combustion, or the process of diffusion—there is often an increase in disorder or the number of microstates available to the system.

For example, in a system where a gas expands into a vacuum or where heat transfers from a hot object to a cold one without external work being applied, the number of accessible microstates increases, leading to a rise in entropy. Irreversible processes are characterized by the fact that they cannot be reversed without external influence, which contributes to the increase in the overall entropy of the system.

In contrast, during reversible processes, the entropy can remain constant, as the system is in equilibrium and can be reversed without altering the overall state. Therefore, the significant takeaway is that irreversible processes are always associated with an increase in entropy, reflecting the natural tendency towards greater disorder in a system