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STD 11 - 5. Thermodynamics and thermochemistry — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 11 - 5. Thermodynamics and thermochemistry4 Marks
MCQ
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 $(\Delta H)$ is zero for isothermal process.
  • A
    If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
  • ✓
    If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
  • C
    If the Assertion is correct but Reason is incorrect.
  • D
    If both the Assertion and Reason are incorrect.
✓

Answer

Correct option: B.
If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
b
In an isothermal process change in internal energy $(\Delta E)$ 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.

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