Question

$K_p=0.04atm$ at 899 K for the equilibrium shown below. What is the equilibrium concentration of $C_2{H}_6$ when it is placed in a flask at 4.0 atm pressure and allowed to come to equilibrium?
$C_2{H}_6\left(g\right)\rightleftharpoons C_2{H}_4\left(g\right)+H_2\left(g\right)$

Answer 1

The initial partial pressures of ethane, ethylene and hydrogen are 4.0 atm, 0 atm and 0 atm respectively.
The equilibrium parial pressures are 4-p atm, p atm and p atm respectively.
The equilibrium constant expression is
$K_c=\frac{P_{C_2{H}_4}{P}_{H_2}}{P_{C_2{H}_6}}=\frac{p\times p}{4-p}=0.04$
$p^2=0.16-0.04p$
$p=0.38$
The equilibrium concentration of ethane is $4-0.38=3.62atm$.