# 7.17     Kp = 0.04 atm at 899 K for the equilibrium shown below. What is the equilibrium concentration of C2H6 when it is placed in a flask at 4.0 atm pressure and allowed to come to equilibrium?                 $C_{2}H_{6}_{(g)}\rightleftharpoons C_{2}H_{4}_{(g)}+H_{2}_{(g)}$

M manish

Suppose the pressure exerted by the hydrogen and ethene gas be $p$ at equilibrium.

the given reaction is-

$C_{2}H_{6}_{(g)}\rightleftharpoons C_{2}H_{4}_{(g)}+H_{2}_{(g)}$
initial pressure                  4 atm              0                     0
At equilibrium                  4 - $p$                 $p$                    $p$

Now,
$K_p = p_{C_2H_4}\times p_{H_2}/p_{C_2H_6}$
$0.04 = \frac{p^2}{4-p}$

By solving the quadratic equation we can get the value of  $p$ = 0.38

Hence,at equilibrium,

$p_{C_2H_6}$ =  4  - p  = 4 -.038

= 3.62 atm

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