For a given chemical reaction $\mathrm{A} \rightarrow \mathrm{B}$ at 300 K the free energy change is $-49.4 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and the enthalpy of reaction is $51.4 \mathrm{~kJ} \mathrm{~mol}^{-1}$. The entropy change of the reaction is ______ $\mathrm{J} \mathrm{K}^{-1} \mathrm{~mol}^{-1}$.

JEE Main · 2021 · 20 Jul 2021 · Shift 2 · Chemical Thermodynamics

For a given chemical reaction

A \to B

at 300 K the free energy change is

- 49.4 kJ mol^{- 1}

and the enthalpy of reaction is

51.4 kJ mol^{- 1}

. The entropy change of the reaction is ______

J K^{- 1} mol^{- 1}

Answer: 336

At constant temperature the Gibbs relation

Δ G = Δ H - T Δ S

rearranges to

Δ S = \frac{Δ H - Δ G}{T}

Both energy terms are in kJ mol

^{- 1}

, and

Δ H - Δ G = 51.4 - (- 49.4) = 100.8

kJ mol

^{- 1}

. Dividing by

T = 300

K gives

0.336

kJ K

^{- 1}

mol

^{- 1}

, that is an entropy change of

336

J K

^{- 1}

mol

^{- 1}

JEE Main · 2021 · 20 Jul 2021 · Shift 2 · Integer answer