Short Answer
U + PV is the best answer.
Thermodynamics questions usually test sign conventions, state variables, or what is being held constant. Before calculating, decide whether the system is exchanging heat, doing work, or both.
H = U + PV; enthalpy accounts for internal energy plus the work needed to establish the system's volume at pressure P.
Why This Answer Is Correct
This is a Medium-level question in Thermodynamics. The prompt is really testing whether you can connect the concept to its defining physical relationship instead of picking a nearby-but-wrong term.
Write the system boundary first. Many thermodynamics mistakes disappear once you know what counts as heat, work, and internal-energy change.
Choices At A Glance
- A. U − TS
- B. U + PV
- C. U − PV
- D. TS − PV
When similar options appear on an exam, eliminate the ones that break the core law, use the wrong units, or confuse a definition with a consequence.
Topic Snapshot
Topic: Thermodynamics
Difficulty: Medium
Best next move: Re-state the governing law in your own words, then solve one more example from the same topic before moving on.