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2. Electrochemistry — Chemistry STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceChemistry2. Electrochemistry1 Mark
MCQ
The variation of equilibrium constant with temperature is given below 

Temperature $\quad$ Equilibrium constant

$\begin{array}{ll} T _{1}=25^{\circ} C & K _{1}=100 \\ T _{2}=100^{\circ} C & K _{2}=100\end{array}$

The values of $\Delta H ^{\circ}, \Delta G ^{\circ}$ at $T _{1}$ and $\Delta G ^{\circ}$ at $T _{2}$ (in $kJ\, mol ^{-1}$ ) respectively, are close to $\left[\right.$ Use $\left. R =8.314\, JK ^{-1} mol ^{-1}\right]$

  • A
    $0.64,-5.71$ and $-14.29$
  • B
    $28.4,-7.14$ and $-5.71$
  • ✓
    $28.4,-5.71$ and $-14.29$
  • D
    $0.64,-7.14$ and $-5.71$
✓

Answer

Correct option: C.
$28.4,-5.71$ and $-14.29$
c
$\operatorname{In}\left[\frac{ k _{2}}{ k _{1}}\right]=\frac{\Delta H ^{\circ}}{ R }\left\{\frac{1}{ T _{1}}-\frac{1}{ T _{2}}\right\}$

$\ln (10)=\frac{\Delta H ^{\circ}}{ R }\left\{\frac{1}{298}-\frac{1}{373}\right\}$

$373 \times 298 \times R \times 2.303=\Delta H ^{\circ}=28.37 kJ mol ^{-1}$

$\Delta G _{ T _{1}}^{\circ}=- RT _{1} \ln \left( K _{1}\right)=-298 R \ln (10)=-5.71 k mol ^{-1}$

$\Delta G _{ T _{2}}^{\circ}=- RT _{2} \ln \left( K _{2}\right)=-373 R \ln (100)$

$=-14.283 kJ / mol$

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