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Chemical Equilibrium question

2019 · 8 Apr · Shift 2 · Q22
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Chemical Equilibrium question

2019 · 8 Apr · Shift 2 · Q22

JEE MainChemistryChemical EquilibriumMCQ+4 / −1
For the following reactions, equilibrium constants are given : SSS(s) + O2O_2O2​(g) ⇋ SO2SO_2SO2​(g); K1 = 1052 2SSS(s) + 3O2O_2O2​(g) ⇋ 2SO3SO_3SO3​(g); K2 = 10129 The equilibrium constant for the reaction, 2SO2SO_2SO2​(g) + O2O_2O2​(g) ⇋ 2SO3SO_3SO3​(g) is :
  1. A
    10181
  2. B
    1025
  3. C
    1077
  4. D
    10154
View written solutionFree

Correct answer: B

  1. Write the given reactions and equilibrium constants

(1)S(s)+O2(g)⇌SO2(g),K1=1052\text{(1)}\quad S(s) + O_2(g) \rightleftharpoons SO_2(g), \qquad K_1 = 10^{52}(1)S(s)+O2​(g)⇌SO2​(g),K1​=1052

(2)2S(s)+3O2(g)⇌2SO3(g),K2=10129\text{(2)}\quad 2S(s) + 3O_2(g) \rightleftharpoons 2SO_3(g), \qquad K_2 = 10^{129}(2)2S(s)+3O2​(g)⇌2SO3​(g),K2​=10129

We need the equilibrium constant for:

(3)2SO2(g)+O2(g)⇌2SO3(g)\text{(3)}\quad 2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)(3)2SO2​(g)+O2​(g)⇌2SO3​(g)


  1. Manipulate the given equations to obtain the target reaction

First, multiply reaction (1) by 2:

2S(s)+2O2(g)⇌2SO2(g)2S(s) + 2O_2(g) \rightleftharpoons 2SO_2(g)2S(s)+2O2​(g)⇌2SO2​(g)

When a reaction is multiplied by 2, its equilibrium constant becomes:

K=(K1)2=(1052)2=10104K = (K_1)^2 = (10^{52})^2 = 10^{104}K=(K1​)2=(1052)2=10104

Now reverse this reaction:

2SO2(g)⇌2S(s)+2O2(g)2SO_2(g) \rightleftharpoons 2S(s) + 2O_2(g)2SO2​(g)⇌2S(s)+2O2​(g)

On reversing, the equilibrium constant becomes:

K=110104=10−104K = \frac{1}{10^{104}} = 10^{-104}K=101041​=10−104


  1. Add this reversed reaction to reaction (2)

Reaction (2):

2S(s)+3O2(g)⇌2SO3(g),K2=101292S(s) + 3O_2(g) \rightleftharpoons 2SO_3(g), \qquad K_2 = 10^{129}2S(s)+3O2​(g)⇌2SO3​(g),K2​=10129

Adding:

2SO2(g)⇌2S(s)+2O2(g)2SO_2(g) \rightleftharpoons 2S(s) + 2O_2(g)2SO2​(g)⇌2S(s)+2O2​(g)

and

2S(s)+3O2(g)⇌2SO3(g)2S(s) + 3O_2(g) \rightleftharpoons 2SO_3(g)2S(s)+3O2​(g)⇌2SO3​(g)

Cancel 2S(s)2S(s)2S(s) from both sides:

2SO2(g)+O2(g)⇌2SO3(g)2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)2SO2​(g)+O2​(g)⇌2SO3​(g)

which is exactly the required reaction.


  1. Calculate the equilibrium constant

For added reactions, equilibrium constants multiply:

K=K2×1(K1)2K = K_2 \times \frac{1}{(K_1)^2}K=K2​×(K1​)21​

Substitute the values:

K=10129×10−104=1025K = 10^{129} \times 10^{-104} = 10^{25}K=10129×10−104=1025


  1. Match with the options

K=1025K = 10^{25}K=1025

So the correct option is:

B: 102510^{25}1025


  1. Comparison with stored correct answer

Stored correct answer: B

Our derived answer: B

Hence, the derived answer agrees with the stored correct answer.

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