Equilibrium and pressure question and change in volume...what's wrong???

Question

I don't understand how to do this question:

An equilibrium mixture contains N_2O_4 (P= 0.26atm) and NO_2 (P=1.2atm) at 350K. The volume of the container is doubled at constant tempreature.

Calculate the equilibrium pressures of N_2O_4 and NO_2 when the system reaches a new equilibrium.

*sorry i dont know how to use subscripts*

Answer 1

I think this problem is just a pressure and volume problem. The problem refers to the mixture as an equilibrium mixture and the equilibrium constant isn't given, so you can assume it is already at equilibrium. What happen is they are changing the volume of an equilibrium mixture. To find the equilibrium pressures you use Boyle's law. We don't know the exact volumes (it really doesn't matter) but we do know the final volume is twice the initial.

First lets find the [N2O4]

Boyle's Law   P1V1 = P2V2

P1 = [N2O4] initial P2 = [N2O4] final

P1 = .26atm V1 = 1L P2 = ? V2 = 2L Solve for P2

(.26atm)(1L) = (P2) (2L)    P2 = [N2O4] final = .13atm

Next lets find [NO2]

P1V1 = P2V2   P1 = [NO2] initial   P2 = [NO2] final

P1 = 1.2atm V1 = 1L  P2 = ? V2 = 2L

(1.2atm)(1L) = (P2)(2L)   P2 = [NO2] final = .6atm

[N2O4] final = .13atm  [NO2] final = .6atm