Question

In an isothermal expansion of an ideal gas, the heat supplied to the gas is:

• A. entirely used to increase internal energy
• B. entirely used to do work
• C. partly used to do work and partly to increase internal energy
• D. none of the above

Hint:

Isothermal means $\Delta U = 0$. Adiabatic means $\Delta Q = 0$.

Answer 1

The Correct Option is B

Step 1: Concept
According to the First Law of Thermodynamics, $\Delta Q = \Delta U + \Delta W$.

Step 2: Meaning
In an isothermal process, the temperature remains constant ($T = \text{constant}$). For an ideal gas, internal energy $U$ depends only on temperature.

Step 3: Analysis
Since $\Delta T = 0$, the change in internal energy $\Delta U = 0$. Therefore, the First Law equation simplifies to $\Delta Q = \Delta W$.

Step 4: Conclusion
All the heat supplied ($\Delta Q$) is converted into work done ($\Delta W$) by the gas during expansion. Final Answer: (B)