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 $\left(△H\right)$ 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. Both Assertion and Reason are incorrect

Answer 1

The correct option is C Assertion is correct but Reason is incorrect

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

Hence, assertion is correct

When $\Delta E=0$ (for isothermal process) $\Delta H$ need not to be zero as work done may or may not be zero.

Hence, option C is correct