Question

In an isothermal process, which of the following remains constant?

• A. Temperature
• B. Pressure
• C. Volume
• D. Heat

Hint:

Remember that in any isothermal process, the system's temperature does not change, which is a key factor in understanding and solving related problems.

Answer 1

The Correct Option is A

Step 1: Read the word isothermal.
The word comes from iso meaning same and thermal meaning heat or temperature. So an isothermal process is one where the temperature stays the same.

Step 2: State the defining feature.
During an isothermal change, the temperature is held fixed from start to end. \[ T = \text{constant} \]

Step 3: Check the internal energy.
For an ideal gas the internal energy depends only on temperature. Since $T$ does not change, the internal energy also does not change. \[ \Delta U = nC_v\Delta T = 0 \]

Step 4: See what can change.
Pressure and volume are free to change as long as their product follows $PV = $ constant. So pressure and volume do vary.

Step 5: See about heat.
Heat is exchanged with the surroundings to keep the temperature steady, so heat is not constant either.

Step 6: State the answer.
Only the temperature stays constant in an isothermal process. \[ \boxed{\text{Temperature}} \]