Question

Which of the following is not a state function?

• A. Internal Energy
• B. Work
• C. Enthalpy
• D. Entropy

Hint:

Remember: \[ \text{State Functions} = U,\ H,\ S,\ G,\ P,\ V,\ T \] \[ \text{Path Functions} = q\ (\text{heat}),\ W\ (\text{work}) \] State functions depend only on the state, whereas path functions depend on the process followed.

Answer 1

The Correct Option is B

A state function only cares about where a system starts and where it ends up, not the road taken to get there. Internal energy, enthalpy and entropy are all like that, if you tell me the initial and final states of a system, their change is fixed no matter how the process was carried out.

Work behaves completely differently. Picture a gas expanding from the same initial volume to the same final volume, once suddenly against vacuum, and once slowly and reversibly. The change in internal energy is identical in both cases, but the work done is not, the reversible path does far more work than the free expansion. That path dependence is exactly what disqualifies work from being a state function.

So among internal energy, work, enthalpy and entropy, the one quantity that depends on the path taken is work. The correct choice is option (2).