JEE Main 2022 · 28 July · evening · Numerical answer · +4 / −0
Among the following the number of state variables is ______________.
Internal energy (U)
Volume (V)
Heat (q)
Enthalpy (H)
Answer and solution
Answer 3
Solution
Chemistry ma’am · 3 steps
Ask of each quantity: does it depend only on where the system is, or on how it got there?
- The test. A state variable has a fixed value for a given state of the system, whatever path was taken to reach it. Its change depends only on the initial and final states.
Quantity Depends on State variable? Internal energy U the state only yes Volume V the state only yes Heat q the path taken no, path function Enthalpy H = U + pV the state only yes - Why heat fails. Heat is energy in transfer, not something a system holds. Going between the same two states by different paths can exchange different amounts of q, so it is a path function.
- So. U, V and H are state variables, giving 3.
The common slip: 4. Counting heat as a state variable gives 4. Heat depends on the path, so it does not count.
The idea to keep. Heat and work are path functions because they describe energy in transit. Anything built from state variables, like H = U + pV, is itself a state variable.
Answer from the NTA final answer key. Solution by PrepWiser.