Which thermodynamic parameter is not a state function :-

Options

A. q at constant pressure
B. q at constant volume
C. w at adiabatic
D. w at isothermal

Answer

To determine which thermodynamic parameter is not a state function, we need to analyze each of the given options. A state function is a property that depends only on the state of the system, not on the path taken to reach that state. In contrast, a path function depends on the specific way a process occurs.

Let's evaluate each option step by step:

1. **Q at constant temperature (ΔH)**:
- At constant temperature, the heat exchanged (Q) is related to the change in enthalpy (ΔH).
- ΔH depends only on the initial and final states of the system.
- Therefore, ΔH is a state function.

2. **Q at constant volume (ΔU)**:
- At constant volume, the heat exchanged (Q) corresponds to the change in internal energy (ΔU).
- ΔU also depends only on the initial and final states of the system.
- Hence, ΔU is a state function.

3. **W at adiabatic process**:
- In an adiabatic process, there is no heat exchange (Q = 0).
- The work done (W) can be expressed using the first law of thermodynamics: ΔU = Q + W.
- Since ΔU depends on the initial and final states, W in an adiabatic process is also determined by these states.
- Thus, W in an adiabatic process is a state function.

4. **W at isothermal process**:
- In an isothermal process, the temperature remains constant.
- The work done (W) depends on the specific path taken during the process (e.g., the volume change).
- Therefore, W at constant temperature is a path function and does not depend solely on the initial and final states.

**Conclusion**:
The thermodynamic parameter that is not a state function is **W at isothermal process** (option D).