KCET · Chemistry · Chemistry in Everyday Life

A reaction has both \( \Delta \mathrm{H} \) and \( \Delta \mathrm{S} \) - ve. The rate of reaction

A increases with increase in temperature
B increases with decrease in temperature
C remains unaffected by change in temperature
D cannot be predicted for change in temperature

Verified Solution

Answer & Solution

Correct Answer

(B) increases with decrease in temperature

Step-by-step Solution

Detailed explanation

The reaction is thermodynamic ally favored when \( \Delta G < 0 \)
\[
\begin{array}{l}
\Delta G=\Delta H-T \Delta S \\
\Delta G=-v e-T(-v e) \\
\Delta G=-v e+T(+v e)
\end{array}
\]
Therefore, on increasing the temperature \( \Delta \mathrm{G} \) becomes positive (+ve). Hence, the rate of reaction increases with
decrease in temperature.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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