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Equilibrium
Combining Equilibrium Constants
1 question from 1 paper, each with its answer.
- question
- 1
- paper
- 1
- of Equilibrium
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Concepts tested
- Manipulating equilibrium constants
All Questions
2003 AIPMT 1 question
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The following equilibria are given :
$N_2 + 3H_2 \rightleftharpoons 2NH_3$, $K_1$
$N_2 + O_2 \rightleftharpoons 2NO$, $K_2$
$H_2 + \dfrac{1}{2}O_2 \rightleftharpoons H_2O$, $K_3$
The equilibrium constant of the reaction $2NH_3 + \dfrac{5}{2}O_2 \rightleftharpoons 2NO + 3H_2O$ in terms of $K_1$, $K_2$ and $K_3$ is :Build the required reaction from the given ones.
Reverse the first reaction: $2NH_3 \rightleftharpoons N_2 + 3H_2$, equilibrium constant $\dfrac{1}{K_1}$
Take the second reaction as it is: $N_2 + O_2 \rightleftharpoons 2NO$, $K_2$
Multiply the third reaction by 3: $3H_2 + \dfrac{3}{2}O_2 \rightleftharpoons 3H_2O$, $K_3^3$
Adding: $2NH_3 + O_2 + \dfrac{3}{2}O_2 \rightleftharpoons 2NO + 3H_2O$, i.e. $2NH_3 + \dfrac{5}{2}O_2 \rightleftharpoons 2NO + 3H_2O$ ($N_2$ and $3H_2$ cancel)
When reactions are added, their equilibrium constants are multiplied:
$K = \dfrac{1}{K_1} \times K_2 \times K_3^3 = \dfrac{K_2K_3^3}{K_1}$