[Rh3333]

I've been working on a challenging problem that asks to find the pressure of a container after two gases have reacted with each other.

The set up is as follows: 2 L of oxygen gas with a pressure of 2 atm is in container 1. 1 L of carbon monoxide at a pressure of 1 atm is held in container 2. The two containers are connected by a valve. What is the pressure of the container once the valve is opened?

What I took into consideration is the fact that carbon monoxide and oxygen gas will react to make carbon dioxide 2CO + O2--> 2CO2. I then thought that if I could find the individual moles of both oxygen and CO gas, I could use the balanced chem. rxn to determine moles of CO2 gas and then calculate the pressure from there (I would do this all using PV=nRT)...but I can't do it that way without knowing the temperature of the system (which is not given).

I then thought to just use initial pressures and molar ratios from the chem. equation to obtain pressure of CO2 gas but that doesn't seem right at all...

Any thoughts as to how to solve this problem? Thanks so much.

[rabolisk]

You assume that the temperature of both containers are equal, and do not change as a result of the chemical reaction. You also assume that the gases behave ideally. (The only way this problem can be solved) You cannot calculate the absolute amounts of oxygen and carbon monoxide present, but you can calculate the relative amounts. From there, use the balanced equation. Remember how ideal gases behave with regards to volume, pressure, etc....

[Rh3333]

You assume that the temperature of both containers are equal, and do not change as a result of the chemical reaction. You also assume that the gases behave ideally. (The only way this problem can be solved) You cannot calculate the absolute amounts of oxygen and carbon monoxide present, but you can calculate the relative amounts. From there, use the balanced equation. Remember how ideal gases behave with regards to volume, pressure, etc....

Thank you that helped a lot! I was able to find a ratio of the moles of oxygen gas to moles of carbon monoxide gas which then allowed me to determine the limiting reagent and the moles of CO2 gas...but I'm kinda stuck. I have relative mole amounts for each gas but still cant figure out how to get to pressure! I was thinking do P1V1/n1=P2v2/n2 and solve for P2 but am not sure what to use for initial p,v and n (and can I still use PV=nRT even though I have n as a relative and not actual value?) Thanks!

[rabolisk]

P1V1/n1 = P2V2/n2 is correct. Good job. Remember that the identity of ideal gases don't matter when talking about total pressure, total volume, and total moles. Hope that helps.