Q10 / 54 · JEE Advanced 2022 (Paper 2) · Chemistry

The correct option(s) about entropy (S) is(are)

[R= gas constant, F= Faraday constant, T= Temperature]

  • A
    For the reaction, Ms+2H+aq→H2g+M2+aq, if dEcell dT=RF then the entropy change of the reaction is R (assume that entropy and internal energy changes are temperature independent).
  • Correct answer
    B
    The cell reaction, Pts∣H2g,1 barH+aq,0.01M‖H+aq,0.1MH2g,1bar∣Pts , is an entropy driven process.
  • Correct answer
    C
    For racemization of an optically active compound, ΔS>0
  • Correct answer
    D
    \(\Delta \mathrm{S}>0\), for \(\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right) 6\right]^{2+}+3 \mathrm{en} \rightarrow[\mathrm{Ni}(\mathrm{en})_{3}]^{2+}+6 \mathrm{H}_2 \mathrm{O}\) (where en \(=\) ethylenediamine)

Solution

(A) Ms+2H+aq→H2g+M2+aq

if dEcell dT=RF

ΔS=nFdEdT=2 FRF=2R

(B) Ecell =-2.303RTFlog0.010.1=2.303RTF

dEcell dT=2.303RF

∴ΔS=nFdEdT>0

It is an entropy driven process.

(C) It is correct

Racemisation is a thermodynamically favourable method, and it proceeds spontaneously if a suitable pathway is accessible for the interconversion of the enantiomers. 

During racemisation of optically active compound, disorderness increases and hence, entropy increases.

(D) For NiH2O62++3en→Nien3+3+6H2O
Entropy increases when bidentate ligands replace monodentate ligands due to increase in the number of molecules on the product side.

Hence, (B, C, D) are correct.

Hence, the correct answer is options: 'B', 'C', 'D'.

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