JEE Main · 2019 · Shift-IImediumCEQ-049

For the reaction 2SO2(g) + O2(g) 2SO3(g), H = -57.2\ kJ\ mol-1 and Kc = 1.7 1016. Which of the following statements is…

Chemical Equilibrium · Class 11 · JEE Main Previous Year Question

Question

For the reaction 2SO2(g)+O2(g)2SO3(g)\mathrm{2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)}, ΔH=57.2 kJ mol1\Delta H = -57.2\ \mathrm{kJ\ mol^{-1}} and Kc=1.7×1016K_c = 1.7 \times 10^{16}. Which of the following statements is incorrect?

Options
  1. a

    The equilibrium constant is large suggestive of reaction going to completion and so, no catalyst is required

  2. b

    The equilibrium will shift in forward direction as the pressure increases

  3. c

    The equilibrium constant decreases as the temperature increases

  4. d

    The addition of inert gas at constant volume will not affect the equilibrium constant

Correct Answera

The equilibrium constant is large suggestive of reaction going to completion and so, no catalyst is required

Detailed Solution

Step 1 — Evaluate each statement:

(1) Large KcK_c \rightarrow no catalyst needed:IncorrectKcK_c being large means the reaction is thermodynamically favorable, but it says nothing about the rate. A catalyst is needed to achieve equilibrium at a practical rate (e.g., V2O5\mathrm{V_2O_5} in Contact process).

(2) Pressure increase \rightarrow forward shift: ✓ Correct — Δng=23=1<0\Delta n_g = 2 - 3 = -1 < 0, so increasing pressure shifts equilibrium forward.

(3) KcK_c decreases with temperature increase: ✓ Correct — reaction is exothermic (ΔH<0\Delta H < 0), so increasing T shifts equilibrium backward Kc\rightarrow K_c decreases.

(4) Inert gas at constant volume \rightarrow no effect: ✓ Correct — partial pressures unchanged.

Answer: Option (1) — Incorrect statement

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For the reaction 2SO2(g) + O2(g) 2SO3(g), H = -57.2\ kJ\ mol-1 and Kc = 1.7 1016. Which of the… (JEE Main 2019) | Canvas Classes