Exams › JEE Main › Chemistry
For a given reversible reaction, both enthalpy change ($\Delta H$) and entropy change ($\Delta S$) are positive. If $T_1$ denotes the equilibrium temperature, under which condition will the reaction be spontaneous?
- $T_1$ is greater than $T$
- $T_1$ is less than $T$
- $T_1$ equals $5T$
- $T$ equals $T_1$
Correct answer: $T_1$ is greater than $T$
Solution
When $\Delta H>0$ and $\Delta S>0$, the reaction becomes spontaneous only at sufficiently high temperature because the $T\Delta S$ term must exceed $\Delta H$. At the equilibrium temperature $T_1$, $\Delta G=0$; for spontaneity, the actual temperature must be higher than the threshold temperature.
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