Question

Nitric oxide is formed in automobile exhaust when nitrogen and oxygen in air react at high temperatures.N2(g) + O2(g) 2NO(g)The equilibrium constant Kp for the reaction is 0.0025 at 2127�C. If a container is charged with 8.00 atm of nitrogen and 5.00 atm of oxygen and the mixture is allowed to reach equilibrium, what will be the equilibrium partial pressure of nitrogen?A) 0.16 atm B) 0.31 atm C) 3.1 atm D) 7.7 atm E) 7.8 atm

Answer 1

Answer : The correct option is, (E) 7.8 atm

Explanation :

The partial pressure of $N_2$ = 8.00 atm

The partial pressure of $O_2$ = 5.00 atm

$K_p$ = 0.0025

The balanced equilibrium reaction is,

                               $N_2(g)+O_2(g)\rightleftharpoons 2NO(g)$

Initial pressure     8.00      5.00            0

At eqm.               (8.00-x) (5.00-x)        2x

The expression of equilibrium constant $K_p$ for the reaction will be:

$K_p=\frac{(p_{NO})^2}{(p_{N_2})(p_{O_2})}$

Now put all the values in this expression, we get :

$0.0025=\frac{(2x)^2}{(8.00-x)\times (5.00-x)}$

By solving the terms, we get:

$x=0.15atm$

The equilibrium partial pressure of $N_2$ = (8.00 - x) = (8.00 - 0.15) = 7.8 atm

Therefore, the equilibrium partial pressure of $N_2$ is 7.8 atm.