Question

Assertion :For an isothermal reversible process $Q=-W$ i.e. work done by the system equals the heat absorbed by the system. Reason: Enthalpy change $\left(\Delta H\right)$ is zero for isothermal process.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

In an isothermal process change in internal energy $\left(\Delta E\right)$ is zero (as it is a function of temperature).
$\therefore$ According to first law of thermodynamics
$\because Q+W=\Delta E$. Hence $Q=-W$ (if $\Delta E=0$)
If a system undergoes a change in which internal energy of the system remains constant (i.e. $\Delta E=0$) then $-W=Q$. This means that work done by the system equals the heat absorbed by the system.

For ideal gas, $\Delta H=n{C}_p\Delta T$ For isothermal process, $\Delta T=0$ hence, enthalpy change must be 0 for ideal gas in isothermal condition.

Hence, option B is correct as both statements are correct but the reason is not the correct explanation.