MCQ
Let us consider a reversible reaction at temperature, T.
In this reaction, both $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ were observed to have positive values. If the equilibrium temperature is Te , then the reaction becomes spontaneous at :
  • A
    $\mathrm{T}=\mathrm{Te}$
  • B
    $\mathrm{Te}>\mathrm{T}$
  • $\mathrm{T}>\mathrm{Te}$
  • D
    $\mathrm{Te}=5 \mathrm{~T}$

Answer

Correct option: C.
$\mathrm{T}>\mathrm{Te}$
(C) $\mathrm{T}>\mathrm{Te}$
For reaction to be spontaneous according to $2^{\text {nd}}$ law:
$\Delta \mathrm{G}<0$
$\Rightarrow \Delta \mathrm{H}-\mathrm{T} \Delta \mathrm{S}<0$
$\Rightarrow \mathrm{T}>\left(\frac{\Delta \mathrm{H}}{\Delta \mathrm{S}}\right)=\mathrm{T}_{\mathrm{e}}$
$\Rightarrow \mathrm{T}>\mathrm{T}_{\mathrm{e}}$

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