Q33 / 125 · BITSAT 2015 · Chemistry

A spontaneous reaction is impossible if

  • A
    both $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ are negative
  • B
    both $\Delta \mathrm{H}$ and $\Delta \mathrm{S}$ are positive
  • C
    $\Delta \mathrm{H}$ is negative and $\Delta \mathrm{S}$ is positive
  • Correct answer
    D
    $\Delta \mathrm{H}$ is positive and $\Delta \mathrm{S}$ is negative

Solution

$\Delta \mathrm{G}=\Delta \mathrm{H}-\mathrm{T} \Delta \mathrm{S} ; \Delta \mathrm{G}$ is positive for a reaction to be non-spontaneous when $\Delta \mathrm{H}$ is positive and $\Delta \mathrm{S}$ is negative.

Hence, the correct answer is option: 'D'.

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