# re-apchem post

posted by on .

a 2L container is charged with 2atm of O2 at 298 Kelvin.
Ch4(g) + 2O2(g) --> CO2(g) + 2H20(g)

calculate the partial pressure of methane needed to react completely with the O2 in the vessel. What is the total pressure after the reaction is complete if the temperature increased to 750 Celcius?
Responses

AP chem - DrBob222, Saturday, April 11, 2009 at 11:54pm
Use PV = nRT
You know P, V, R, and T, calculate n for oxygen.
That allows you to calculate CH4 moles and from there moles CO2 and moles H2O.
Then calculate total P from new conditions for PV = nRT.

NEW:

once I have calculated the number of moles, how do i calculate the partial pressure of methane needed to completely react with O2? is that the number of moles?

I have you need .0817 moles of methane but i don't know if this is the same as partial pressure
Responses

ap chem repost - DrBob222, Sunday, April 12, 2009 at 8:20pm
No, moles isn't the same thing as partial pressure. I obtained an answer of 0.0818 moles CH4 needed.
Now use PV = nRT again.
You know V, R, n, and T (but T is different at the new conditions); calculate P of CH4 and that will be the partial pressure of CH4. (By the way, note the correct spelling of Celsius.)

I got 3.44 atm for the partial pressure of methane, then to get the total pressure after the reaction is complete if the temperature has increased to 750C, do I add up the moles and plug this in for n in PV=nRT?

Thank you

• re-apchem post - ,

Yes and no. You add the moles CO2 to moles H2O and use that for n but there should be no CH4 or O2 remaining if all of the CH4 and O2 have reacted. Moles H2O will be twice that of CO2.