Question

15.0 moles of gas are in a 4.00 L tank at 21.2 ∘C . Calculate the difference in pressure between methane and an ideal gas under these conditions. The van der Waals constants for methane are a=2.300L2⋅atm/mol2 and b=0.0430 L/mol.

Answer 1

For this problem, you have to use Van der Waals equations to find the pressure of methane and then subtract the ideal gas pressure.

(P+(an^2/v^2))(V-nb)=nRT
(P+2.3(15^2)/(4^2))(4-(15*0.043))=15*0.0821*294.2
(P+32.34)(3.355)=362.31

P=75.65 atm
So, the pressure for methane gas is 75.65 atm.

Next, you find the ideal gas pressure by using ideal gas formula.
PV=nRT
P(4)=15(0.08206)(294.2)
P=90.58 atm

Now, you subtract ideal gas pressure from the pressure of methane.
(75.65-90.58)atm=-14.93atm