If for a certain reaction Δ _ r H is 30 kJmol ^ - 1 at 450K, the value of Δ _ r S (in JK ^ - 1 mol ^ - 1 ) for which the same reaction will be spontaneous at the same temperature is

Correct answer: A. 70 Δ G = Δ H - T Δ S For spontaneous, - T > ( )/(T) > 30 × 10 ^ 3 Jmol ^ - 1 450K > 66 . 6 Jmol ^ - 1 K ^ - 1 (Check by options) So, option (1) , i.e. (70 ~J mol^ -1 ~K^ -1 ) satisfies it.

NEET 2020

Exam: NEET
Year: 2020
Subject: Chemistry
Chapter: Thermodynamics (C)

NEET 2020 · Chemistry · Thermodynamics (C)

If for a certain reaction Δ _ r H is 30 kJmol ^ - 1 at 450K, the...

If for a certain reaction

{\Delta}_{r}H

30{kJmol}^{- 1}

450K,

the value of

{\Delta}_{r}S

(in

{JK}^{- 1}{mol}^{- 1}

) for which the same reaction will be spontaneous at the same temperature is

Options

A $70$
B $- 33$
C $33$
D $- 70$

Correct answer

A. $70$

Step-by-step solution

$\Delta G = \Delta H - T \Delta S$
For spontaneous,

$\DeltaG < 0$
$\DeltaH - T\DeltaS < O$
$\DeltaS > \dfrac{\DeltaH}{T}$
$\DeltaS > \dfrac{30 \times {10}^{3}{Jmol}^{- 1}}{450K}$
$\DeltaS > 66 . 6{Jmol}^{- 1}{K}^{- 1}$ (Check by options)

So, option (1) , i.e. (70 \mathrm{~J} \mathrm{mol}^{-1} \mathrm{~K}^{-1}) satisfies it.

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