Can entropy change be zero?

Yes, entropy change can indeed be zero under certain conditions. Entropy is a measure of the disorder or randomness of a system, and it tends to increase in closed systems over time according to the second law of thermodynamics. However, there are scenarios where entropy change can be zero:

Reversible Processes: In a reversible process, entropy change can be zero. Reversible processes are idealized and typically occur in thermodynamic equilibrium, where the system and its surroundings can be returned to their original states without any net change in entropy.

Phase Transitions at Critical Points: At the critical point of a phase transition, such as the boiling point of a liquid or the melting point of a solid, entropy change can be zero. At these points, the distinction between phases becomes less clear, and entropy change can level off.

Adiabatic Processes: In an adiabatic process, no heat is exchanged with the surroundings. If the system is also isolated (i.e., no matter or energy exchange with the surroundings), the entropy change of the system can be zero.

Isothermal Processes in Ideal Gases: In an ideal gas undergoing an isothermal expansion or compression, the entropy change can be zero if the temperature remains constant throughout the process. This is because the change in entropy is related to the heat transfer, and in an isothermal process, the heat transfer compensates for the entropy change.

In summary, while entropy generally tends to increase in closed systems, there are specific conditions and processes where the entropy change can be zero.