Question

The enthalpy and entropy of a reaction are $-5.0 \, kJ/mol$ and $-20 \, JK^{- 1} \, mol^{- 1}$ respectively and are independent of temperature. What is the highest temperature upto which the reaction is feasible?

• A. 250 K
• B. 240 K
• C. 275 K
• D. 300 K

Answer 1

Answer: (A)

Both $\Delta H$ and $\Delta S$ are negative and, therefore, the given reaction will be spontaneous $\left(\right.\Delta G < 0\left.\right)$ if

$\Delta H-T\Delta S < 0$

or $-5.0 \, kJ-T\left(\right.-20 \, JK^{- 1}\left.\right) < 0$

or $-5.0\times 10^{3} \, J+T\left(\right.20 \, JK^{- 1}\left.\right) < 0$

i.e., $T < \frac{5 \times 1 0^{3} \, J}{20 \, J K^{- 1}} < 250 \, K$ .