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Law of Chemical Equilibrium
Concepts tested here
- Writing the equilibrium constant expression
All Questions
2006 AIPMT-PRE 1 question
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For the reaction :
$CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(l)$
$\Delta H_r = -170.8$ kJ mol$^{-1}$
Which of the following statements is not true :-In the expression of the equilibrium constant, each concentration (or partial pressure) is raised to the power of its stoichiometric coefficient, and pure liquids and solids are left out.
For $CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(l)$, the coefficient of $O_2$ is 2 and $H_2O$ is a pure liquid.
So the correct expression is $K_P = \dfrac{p_{CO_2}}{p_{CH_4}\,(p_{O_2})^2}$
The expression given, $\dfrac{[CO_2]}{[CH_4][O_2]}$, does not have the square on the oxygen term, so that statement is not true.
$\Delta H_r$ is negative, so the reaction is exothermic; that statement is true.
By Le Chatelier's principle, adding a reactant ($CH_4$ or $O_2$) shifts the equilibrium to the right; that statement is true.
The concentrations of gaseous $CO_2$ and liquid $H_2O$ are not equal; that statement is also true.