For reversible process at equilibrium, the change in entropy may be expressed as

Options

A. Positive
B. negetive
C. Zero
D. none of these

Answer

To solve the question regarding the change in entropy for a reversible process at equilibrium, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Entropy Change**:
- The change in entropy (ΔS) is a measure of the disorder or randomness in a system. For a reversible process at equilibrium, we need to express this change mathematically.

2. **Defining the Process**:
- A reversible process is one that can be reversed without leaving any trace on the surroundings. At equilibrium, the system is in a state where there are no net changes occurring.

3. **Heat Transfer in Reversible Processes**:
- For a reversible process, the heat absorbed (Q) by the system can be expressed in terms of the temperature (T) at which the heat is absorbed.

4. **Using the Formula for Entropy Change**:
- The change in entropy can be defined as:
\[ \Delta S = \frac{Q}{T} \]
- Here, ΔS is the change in entropy, Q is the heat absorbed by the system, and T is the absolute temperature at which the heat is absorbed.

5. **Conclusion**:
- Therefore, for a reversible process at equilibrium, the change in entropy can be expressed as:
\[ \Delta S = \frac{Q}{T} \]
- This indicates that the change in entropy is directly proportional to the heat absorbed and inversely proportional to the temperature.

### Final Answer:
The change in entropy for a reversible process at equilibrium may be expressed as \( \Delta S = \frac{Q}{T} \).

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