**Entropy**

Entropy is the property of a working system that changes as heat is supplied to the working fluid in a reversible manner. It is a measure of the disorder or randomness in a system. The concept of entropy is closely related to the second law of thermodynamics, which states that the entropy of an isolated system always tends to increase over time.

**Explanation:**

When heat is supplied to a working fluid in a reversible manner, the entropy of the system increases. This means that the disorder or randomness in the system increases. Reversible heat transfer refers to a process in which the heat is transferred to the system in such a way that the system can be brought back to its original state by reversing the process without leaving any trace.

**Importance of Reversibility:**

Reversible processes are idealized processes that are used as a benchmark for comparison with real processes. In reality, most processes are irreversible to some extent, and irreversible processes are associated with an increase in entropy.

**Relationship between Heat and Entropy:**

The relationship between heat and entropy can be expressed mathematically using the equation:

∆S = Q/T

Where ∆S is the change in entropy, Q is the heat supplied to the system, and T is the temperature at which the heat transfer occurs. This equation shows that the change in entropy is directly proportional to the amount of heat supplied and inversely proportional to the temperature at which the heat transfer occurs.

**Conclusion:**

Entropy is a property of a working system that changes as heat is supplied to the working fluid in a reversible manner. It is a measure of the disorder or randomness in a system. Reversible heat transfer leads to an increase in entropy, while irreversible processes are associated with an increase in entropy. The relationship between heat and entropy is given by the equation ∆S = Q/T, where ∆S is the change in entropy, Q is the heat supplied to the system, and T is the temperature at which the heat transfer occurs.