question_answer

For the reaction,

\[C{{H}_{4}}(g)+2{{O}_{2}}(g)\rightleftharpoons C{{O}_{2}}(g)+2{{H}_{2}}O(\ell )\,,\]\[{{\Delta }_{r}}H=-170.8\,kJ\,mo{{l}^{-1}}\]

Which of the following statements is not true?                                                                    [AIPMT (S) 2006]

A)  At equilibrium, the concentrations of \[C{{O}_{2}}\,(g)\] and \[{{H}_{2}}O\,(l)\] are not equal

B)              The equilibrium constant for the reaction is given by \[{{K}_{p}}=\frac{[C{{O}_{2}}]}{[C{{H}_{4}}][{{O}_{2}}]}\]

C)       Addition of \[C{{H}_{4}}\left( g \right)\] or \[{{O}_{2}}(g)\] at equilibrium will cause a shift to the right

D)       The reaction is exothermic

Correct Answer: B

Solution :

For the reaction,

This equilibrium is an example of heterogeneous chemical equilibrium. Hence, for it

(Equilibrium constant on the basis of conc.)

and

(Equilibrium constant according to partial pressure)

Thus in it concentration of CO2 (g) and H2O (l) are not equal at equilibrium

The equilibrium constant

not correct expression

In addition of CH4(g) or O2(g) at equilibrium Kc will be decreased according to expression (i) but Kc remains constant at constant temperature for a reaction, so for maintaining the constant value of Kc, the concentration of CO2 will increased in same order. Hence, on addition of CH4 or O2 equilibrium will cause to the right. This reaction is an example of exothermic reaction.