JEE Main · 2020 · Shift-IhardTHERMO-135

The variation of equilibrium constant with temperature is given below: | Temperature | Equilibrium Constant |…

Thermodynamics · Class 11 · JEE Main Previous Year Question

Question

The variation of equilibrium constant with temperature is given below:

| Temperature | Equilibrium Constant | |-------------|---------------------| | T1=25CT_1 = 25^\circ\text{C} | K1=10K_1 = 10 | | T2=100CT_2 = 100^\circ\text{C} | K2=100K_2 = 100 |

The values of ΔH\Delta H^\circ, ΔG\Delta G^\circ at T1T_1 and ΔG\Delta G^\circ at T2T_2 (in kJ mol1\text{kJ mol}^{-1}) respectively, are close to [use R=8.314JK1mol1R = 8.314\,\text{JK}^{-1}\text{mol}^{-1}]

Options
  1. a

    28.4,  7.1428.4,\;-7.14 and 5.71-5.71

  2. b

    0.64,  7.140.64,\;-7.14 and 5.71-5.71

  3. c

    28.4,  5.7128.4,\;-5.71 and 14.29-14.29

  4. d

    0.64,  5.710.64,\;-5.71 and 14.29-14.29

Correct Answera

28.4,  7.1428.4,\;-7.14 and 5.71-5.71

Detailed Solution

🧠 Van't Hoff gives ΔH\Delta H^\circ; then ΔG=RTlnK\Delta G^\circ = -RT\ln K at each temperature The integrated Van't Hoff equation links the ratio of equilibrium constants at two temperatures to the standard enthalpy change.

🗺️ Calculation lnK2K1=ΔHR(1T11T2)\ln\frac{K_2}{K_1} = \frac{\Delta H^\circ}{R}\left(\frac{1}{T_1} - \frac{1}{T_2}\right)

ln10=ΔH8.314(12981373)\ln 10 = \frac{\Delta H^\circ}{8.314}\left(\frac{1}{298} - \frac{1}{373}\right)

2.303=ΔH8.314×6.75×1042.303 = \frac{\Delta H^\circ}{8.314} \times 6.75 \times 10^{-4}

ΔH=2.303×8.3146.75×104=28,370J mol128.4kJ mol1\Delta H^\circ = \frac{2.303 \times 8.314}{6.75 \times 10^{-4}} = 28{,}370\,\text{J mol}^{-1} \approx 28.4\,\text{kJ mol}^{-1}

ΔG\Delta G^\circ at T1=298KT_1 = 298\,\text{K}: =(8.314)(298)(2.303)=5706J5.71kJ mol1= -(8.314)(298)(2.303) = -5706\,\text{J} \approx -5.71\,\text{kJ mol}^{-1}

ΔG\Delta G^\circ at T2=373KT_2 = 373\,\text{K}: =(8.314)(373)(4.606)=14,280J14.3kJ mol1= -(8.314)(373)(4.606) = -14{,}280\,\text{J} \approx -14.3\,\text{kJ mol}^{-1}

⚠️ Data note: The calculation gives 28.428.4, 5.71-5.71, 14.3-14.3 which matches option (c). The stored correct option is (a); verify against the original source.

Answer: 28.4, -5.71, -14.3 kJ mol1\boxed{\text{Answer: 28.4, -5.71, -14.3 kJ mol}^{-1}}

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