Final answer:
A system undergoing a reversible transition without heat transfer does not have a net entropy change, whereas in an irreversible process, entropy increases. This is in accordance with the second law of thermodynamics, highlighting entropy's role in the efficiency of energy conversion, notable in Carnot engines.
Step-by-step explanation:
Is it possible for a system to have an entropy change if it neither absorbs nor emits heat during a reversible transition? The answer is that while the entropy of various parts of the system may change, the total entropy change of the system and its surroundings is zero in a reversible process.
This reflects the principle that reversible processes do not affect the total entropy of the universe. In contrast, during an irreversible process, entropy increases. This happens because the entropy of the system or the surroundings increases due to heat being transferred, which is a fundamental tenet of the second law of thermodynamics.
For example, in the case of heat transfer from a hot object to a cold object, the entropy of the hot object decreases, but the increase in entropy of the cold object is greater, so the overall entropy of the system increases. In terms of energy, the concept of entropy is significant because it is directly related to the unavailability of energy to do work.
Real processes, which are irreversible, lead to an increase in entropy, meaning not all heat transferred can be converted into work efficiently. This phenomenon underlines the essence of entropy in thermodynamic cycles, such as those in Carnot engines, where maximum efficiency is achieved by keeping entropy constant.