# 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? - Chemistry

#### Question

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?

C2H6 (g) ⇌ C2H4 (g) + H2 (g)

#### Solution

Let p be the pressure exerted by ethene and hydrogen gas (each) at equilibrium.

Now, according to the reaction,

C_2H_(6(g)) ↔   C_2H_(4(g))      + H_(2(g))

Initial conc              4.0 atm                  0                      0

At equilibrium        4.0 - p                    p                      p

We can write,

(p_(C_2H_4) xx p_(H_2))/p_(C_2H_6) = K_p

=> (p xx p)/(4.0 - p) = 0.04

=> p^2 + 0.16 - 0.04 p

=> p^2 + 0.04 p - 0.16 = 0

Now p = (-0.04 +- sqrt((0.04)^2 - 4xx1xx (-0.16)))/(2xx1)

= (-0.04 +- 0.80)/2

= 0.76/2 (Taking positive value)

= 0.38

Hence, at equilibrium,

[C_2H_6] - 4 - p

= 4 - 0.38

= 3.62 atm

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