Equilibrium Concentrations -- A + B = 2C?

Question

At a particular temperature, Kp = 0.390 for the reaction

N2O4(g) = 2NO2(g)

A flask containing only NO2(g) at an initial pressure of 9.60 atm is allowed to reach equilibrium. Calculate the total pressure in this flask at equilibrium.



With no change in the amount of material in the flask, the volume of the container in question is increased to 2.000 times the original. Assuming constant temperature, calculate the (new) total pressure, at equilibrium.

Answer 1

This is NOT a "A + B = 2C" kind of reaction.
---------N2O4(g) = 2NO2(g)
Initial: 0--------------9.60
final:--X-------------(9.60-2X)
Kp = 0.390 = (9.60-2X)^2/ X
4X^2 - 38.40X-0.390X + 9.60^2 = 0
X1=5.53(to be omitted--do you know why?)
X2 = 4.16
The total pressure in this flask at equilibrium is (9.60-4.16)atm or 5.44 atm.

Assume volume increased before reaction. Thus the initial pressure of NO2(g) is (9.60/2000)atm or 0.0048 atm.
---------N2O4(g) = 2NO2(g)
Initial: 0--------------0.0048
final:--X-------------(0.0048-2X)
Kp = 0.390 = (0.0048-2X)^2/ X
4X^2 - 0.0192X-0.390X + 0.0048^2 = 0
X1=0.102(to be omitted--do you know why?)
X2=5.63x10^-5
The total pressure in this flask at equilibrium is (0.00480 - 5.63x10^-5) atm or 0.00474 atm.