physics
posted by paro on .
0.11 mol of argon gas is admitted to an evacuated 50cm^3 container at 10 degree C. The gas then undergoes an isothermal expansion to a volume of 200cm^3.
What is the final pressure of the gas?

In isothermal expansions, the product
P*V = a constant. Therefore
P2/P1 = V1/V2 = 50/200 = 1/4
Since you were not told the initial pressure P1, you will have to use the perfect gas law and the information given.
0.11 moles at STP (1 atm and 273K) occupies 0.11*22.4 = 2.46 liters. At 10C (283K) it would occupy 2.55 liters. Since the initial volume is only 50 cm^3 = 0.05 l, the initial pressure must be
P1 = 2.55/0.05 = 51 atm.
The final pressure is 1/4 of that.
You could also have used P = nRT/V to get the initial pressure. Personally I find it easier to remember that 1 mole is 22.4 liters at STP. There are too many values of R, with different units, to try to remember.