Finding the amount of heat required to double volume?

[charmedbeauty]

Homework Statement

In an experiment, 1.35 mol of oxygen (0₂) are heated at constant pressure starting at 11.0°C. How much heat must be added to the gas to double its volume? You may assume without proof, that the molar specific heats are c_p=7R/2 and c_v=5R/2.

Homework Equations

The Attempt at a Solution

My working so far...

Q=nC_pΔT

Q=n(7R/2)ΔT

Q= 1.35(7R/2)(s-11) -----> where s= T_f

But I need some equation linking change in volume to this...

ie Q= -PΔV

But I don't Know what P is?

Perhaps I need something with ΔE_int but I am not to sure.
I was thinking I will need to solve the first equation simultaneously with one with ΔV

I'm stuck as to where to go from here??

Please help any advice is greatly noted.

 

[LawrenceC]

Hint: Use the ideal gas law followed by a conservation of mass.