IB Physics B.4.2 Entropy and System Evolution Key Definitions

Entropy is a measure of the disorder or randomness in a system. It quantifies the number of possible ways a system can be arranged.

Irreversible processes are real-world processes that cannot be undone without leaving a net change in the system or surroundings.

Reversible processes are idealized processes that occur in such a way that the system and its surroundings can be returned to their original states without any net change.

The second law of thermodynamics states that in any natural process, the total entropy of an isolated system always increases or remains constant in ideal reversible processes.