For isothermal expansion , which is true?

Options

A. `Delta P = 0`
B. `Delta S = 0`
C. `Delta G = 0`
D. `Delta U = 0`

Answer

To solve the question regarding isothermal expansion and determine which statement is true, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Isothermal Expansion**:
- Isothermal expansion refers to a process in which a gas expands at a constant temperature. The term "isothermal" means that the temperature (T) remains constant throughout the process.

2. **Recognize the Implications of Constant Temperature**:
- Since the temperature is constant, the change in temperature (ΔT) is zero. This is a key point because it directly affects the internal energy of the system.

3. **Relate Internal Energy to Temperature**:
- The internal energy (U) of an ideal gas is a function of temperature. For an ideal gas, the internal energy is directly proportional to the temperature. Therefore, if the temperature does not change, the internal energy also does not change.

4. **Calculate the Change in Internal Energy**:
- Since ΔT = 0, it follows that the change in internal energy (ΔU) is also zero. Mathematically, this can be expressed as:
\[ \Delta U = U_{\text{final}} - U_{\text{initial}} = 0 \]
- Thus, we conclude that:
\[ \Delta U = 0 \]

5. **Identify the Correct Statement**:
- Based on the above reasoning, the correct statement regarding isothermal expansion is that the change in internal energy (ΔU) is equal to zero. This corresponds to option D in the question.

### Final Answer:
The correct statement for isothermal expansion is:
- **ΔU = 0** (The change in internal energy is zero).