A completely empty 2.00 L reaction vessel is filled with ammonia gas (NH3) at a constant temperature of 611K. The initial partial pressure of NH3 was 6.40 atm.

Question

With time it partially decomposed according to the reaction below until equilibrium was reached:

     

At equilibrium, the total pressure inside the flask was 9.40 atm. 

What is the numerical value of Kp for this reaction at this temperature?

Answer 1

2NH₃(g) <===> 3H₂(g) + N₂(g)

6.40....................0................0.........I

-2x...................+3x..............+x........C

6.40-2x.............3x.................x........E

@equilibrium we are told that total pressure (6.4-2x + 3x + x) = 9.40 atm

From this info, we can find the value of x...

6.40 +2x = 9.40 atm

x = 1.5 atm

@ equilibrium, we have the following partial pressures:

(H₂) = 3 x 1.5 = 4.5 atm

(N₂) = 1.5 atm

(NH₃) = 6.40 - 3 = 3.40 atm

Kp = (H₂)³(N₂) / (NH₃)² = (4.5)³(1.5) / (3.40)²

Kp = 11.8