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: Understanding the Concept
The first law is \(\Delta U=Q+W\), with work taken as work done on the system.

Step 2: Isothermal condition
For an isothermal process of an ideal gas the temperature is constant, so \(\Delta U=0\).

Step 3: Result
Then \(Q+W=0\), which gives \(W=-Q\). The heat absorbed equals the work done by the gas.

Final Answer:
For an isothermal process \(W=-Q\). \[ \boxed{\text{(A) }W=-Q} \]