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5. Thermodynamics and thermochemistry — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistry5. Thermodynamics and thermochemistry1 Mark
MCQ
Assertion :For a reaction $2NH_3 (g) \to N_2 (g) + 3H_2 (g)$ ; $\Delta H > \Delta E$
Reason : Enthalpy change is always greater than internal energy change.
  • A
    If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
  • B
    If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
  • ✓
    If the Assertion is correct but Reason is incorrect.
  • D
    If both the Assertion and Reason are incorrect.
✓

Answer

Correct option: C.
If the Assertion is correct but Reason is incorrect.
c
For given reaction $\Delta H> \Delta E $ because $\{ \Delta H = \Delta E + \Delta nRT\} $. In this reaction $\Delta {n_{(g)}}$ is $[(3 + 1) - 2 =  + 2]$ so $\Delta H > \Delta E$. 

Thus, assertion is true.

In some cases, the enthalpy change may be less than internal energy change (in these cases $\Delta n_{(g)}$, is negative), so the reason is false. 

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