Entropy is a measure of randomess of system. When a liquid is converted to the vapour state entropy of the system increases. Entropy in the phase transformation is calculated using `Delta S = (Delta H)/(T)` but in reversible adiabatic process `Delta`S will be zero. The rise in temperature in isobaric or isochoric process increases the randomness of system, which is given by
`Delta S = "2.303 n C log"((T_(2))/(T_(1)))`
`C = C_(P) or C_(V)`
Entropy change in a reversible adiabatic process is

Options

A. Zero
B. Always positive
C. Always negative
D. Sometimes positive and sometimes negative

Answer

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

### Step 1: Understanding the Concept of Entropy
Entropy (ΔS) is a measure of the randomness or disorder of a system. In general, when a system undergoes a change, the entropy can either increase or decrease depending on the nature of the process.

**Hint:** Recall that entropy is related to the amount of energy dispersal in a system.

### Step 2: Analyzing the Reversible Adiabatic Process
In a reversible adiabatic process, there is no heat exchange with the surroundings. This means that the heat (Q) transferred is equal to zero.

**Hint:** Remember that "adiabatic" means no heat transfer occurs.

### Step 3: Applying the Formula for Entropy Change
The change in entropy for a reversible process is given by the formula:
\[ \Delta S = \frac{Q_{\text{reversible}}}{T} \]
Since we are dealing with an adiabatic process where \(Q = 0\), we can substitute this into the equation.

**Hint:** Think about what happens to the equation when Q is zero.

### Step 4: Conclusion on Entropy Change
Substituting \(Q = 0\) into the entropy change formula, we have:
\[ \Delta S = \frac{0}{T} = 0 \]
Therefore, the entropy change (ΔS) in a reversible adiabatic process is zero.

**Hint:** Consider what this implies about the randomness of the system during an adiabatic process.

### Final Answer
The entropy change in a reversible adiabatic process is:
**Option A: 0**