A process that has $\Delta \mathrm{H}=200 \mathrm{~J} \mathrm{~mol}^{-1}$ and $\Delta \mathrm{S}=40 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$. Out of the values given below, choose the minimum temperature above which the process will be spontaneous:

JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Chemical Thermodynamics

A process that has

Δ H = 200 J mol^{- 1}

and

Δ S = 40 JK^{- 1} mol^{- 1}

. Out of the values given below, choose the minimum temperature above which the process will be spontaneous:

Answer: (C)

A process turns spontaneous when

Δ G = Δ H - T Δ S

drops below zero, and the crossover is at

Δ G = 0

, i.e.

T = \frac{Δ H}{Δ S}

. Here that is

\frac{200}{40} = 5

K, and above it the

T Δ S

term overtakes

Δ H

so that

Δ G < 0

. So the lowest temperature at which the process becomes spontaneous is

5

JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Single correct option