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)}

Answers (1)
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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