Pressure problem using 2 different amounts?

Question

Problem from the back of my book. I have the answer but not sure how to work it.

A quantity of N2 gas originally held at 4.62 atm pressure in a 1.70-L container at 26°C is transferred to a 13.5-L container at 20.0°C. A quantity of O2 gas originally at 3.34 atm and 26.0°C in a 8.43-L container is transferred to this same container. What is the total pressure in the new container?

Answer 1

The total pressure will be the sum of the partial pressures of the 2 components.

One way to do this is :

First, determine moles of the two components; Remember T in Kelvin 26 C = 299K, P in atm, V in liters! n = PV/RT:

for N2: (4.62atm x 1.70L)/(299K x 0.08206Latm/molK) =

0.318mole N2

For O2: (3.34atm x 8.43L)/(299K x 0.08206Latm/molK) =

1.15mole O2

Now we have total moles, T, & V are given, so solve for P. Watch out ! The new T is 20.0 C, V is now 13.5L

P = nRT/V

P = (0.318 + 1.15)mol x 0.08206Latm/molK x (20 +

273K)/13.5L

= 2.61 atm