Posted by
**Lori** on
.

15.0 moles of gas are in a 6.00L tank at 298.15K. Calculate the difference in pressure between methane and an ideal gas under these conditions. The van der Waals constants for methane are a=2.300 L^2*atm/mol^2 and b=0.0430 L/mol.

I found the idea gas pressure to be 61.2 atm by using the ideal gas law. However I can't seem to get the right value for the pressure of methane. Below are my workings, can anyone see what I'm doing wrong?

P= [(nRT)/(V-nb)] - [(an)^2/V^2]

P=[(15 mol*0.08206*298.15K)/(6.00L-(15mol*0.0430)] -[(15mol*2.3)^2/(6.00L)^2]

P=68.53-33.06

P=35.47 atm