Question

Consider a reaction for which ΔH = 6.03 kJ/mol; ΔS = 22.1 J/K-mol. Which of the following statements is true?

a. The reaction becomes spontaneous at high temperatures above 273 K

b. The reaction becomes spontaneous at low temperatures below 273 K

c. The reaction is spontaneous at all temperatures

d. The reaction is never spontaneous

Answer 1

Reaction becomes spontaneous when $\Delta S > 0 , \Delta G < 0$

In our case change in entropy is already > 0. Now for Change in Gibb's free energy to be less than zero,

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

$\therefore \Delta H <T\Delta S$

Substitute values,

6.03 * 1000 < T*22.1

Therefore T > 273 K. For temperatures greater than 273 K, reaction becomes spontaneous.

Answer would be (a)