Dinitrogen tetroxide decomposes according to N2O4 (g) = 2NO2 (g)

Question

In a certain experiment, N2O4(g) at an initial pressure of 0.554 bar is introduced into an empty reaction container; after equilibrium is established, the total pressure is 0.770 bar. A quantity of NO2(g) is injected into the container and the total pressure jumps to 0.906 bar. Calculate the total pressure after equilibrium is reestablished.

I need help setting up this problem. Please help.

Answer 1

I would do this.
............N2O4 ==> 2NO2
initial..0.554.........0
change....-p..........+2p
equil....0.554-p.......2p

Total P @ equil = 0.770; therefore,
0.554-p+2p = 0.770 and this allows you to calculate Kp.

NO2 is injected to make Ptotal = 0.906 bar so that makes 0.906-0.770 = 0.136 bar injected.
I would make a new ICE chart with NO2 start = 0.136 + old equil pressure and N2O4 = old equil and recalculate new pressures using the Kp from the first part. You know, of course that the reaction will be shifted to the left.