Question

Which of the following is applicable for isothermal process?

• A. \(W=-Q\)
• B. \(-\Delta U=-W\)
• C. \(\Delta U=Q_{v}\)
• D. \(Q_{p}=\Delta U+P_{ext}\Delta V\)

Hint:

In an isothermal process the temperature is constant, so the internal energy change is zero and the first law gives heat equal to work.

Answer 1

The Correct Option is A

Step 1: Compare the options
Option (C), $\Delta U=Q_v$, holds for a constant-volume process. Option (D) is the form for a constant-pressure process.

Step 2: Check option B
Option (B), $-\Delta U=-W$, means $\Delta U=W$, which holds for an adiabatic process where $Q=0$.

Step 3: Select
Only $W=-Q$ follows from $\Delta U=0$, so option (A) is correct.

Final Answer:
The relation is $W=-Q$. \[ \boxed{\text{(A) }W=-Q} \]