The reaction: $\mathrm{MgO}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \rightarrow \mathrm{Mg}(\mathrm{s})+\mathrm{CO}(\mathrm{g})$, for which $\Delta_{\mathrm{r}} \mathrm{H}^{0}=+491.1 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $\Delta_{\mathrm{r}} \mathrm{S}^{0}=198.0 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$ is not feasible at 298 K . Temperature above which reaction will be feasible is:

JEE Main · 2019 · 11 Jan 2019 · Shift 2 · Chemical Thermodynamics

The reaction:

MgO (s) + C (s) \to Mg (s) + CO (g)

, for which

Δ_{r} H^{0} = + 491.1 kJ mol^{- 1}

and

Δ_{r} S^{0} = 198.0 JK^{- 1} mol^{- 1}

is not feasible at 298 K . Temperature above which reaction will be feasible is:

Answer: (C)

The reaction turns spontaneous when

Δ G^{\circ} = Δ H^{\circ} - T Δ S^{\circ}

reaches zero. Setting

0 = 491.1 \times 1 0^{3} - T \times 198

gives

T = \frac{491100}{198} \approx 2480

K, above which

Δ G^{\circ}

becomes negative and the reaction proceeds.

JEE Main · 2019 · 11 Jan 2019 · Shift 2 · Single correct option