Answer:
Explanation:
An isentropic process is one that does not change the entropy of the system. A reversible of the universe, and it is reversible because of that. Real processes increase the entropy of the universe, so trying to reverse them would decrease the entropy of the universe, which is impossible, so they are irreversible.
The Carnot cycle has 4 phases:
-Isotermal expansion of gas. In this process it takes heat from a hot source. It is a reversible process, but not isentropic.
-Adiabatic expansion. This one is isentropic, the entropy of the gas remains constant and it doesn't interact with the surroundings. The gas expands not by its own, but the machine makes it expand (it pulls on the gas). The gas cools down.
-Isotermal compression. Reversible but not adiabatic. The gas exchanges heat with the cold source, reducing its volume.
-Adiabatic compression. Adiabatic and isentropic. The machine compresses the gas, causing it to heat up.
