At high pressures, real gases do not behave ideally. calculate the pressure exerted by 18.0 g h2 at 20.0°c in a 1.00 l container assuming in part 1 non-ideal behavior and in part 2 ideal behavior.

Part 1 (non-ideal behavior ):
we will use Van der Waals formula:
P = (nRT/(V-nb)) - (n^2 a/V2)
when n (moles of H2) = 18 g / 2 = 9 moles
R (constant) = 0.0821
T(tempreature in kelvin = 20 +273 = 293 K
V(Volume) = 1 L
a (constant for H2) = 0.2476
b(constant for H2) = 0.02661
So by substitution:
∴P = (9*0.0821*293/(1-(9*0.02661))) - (9^2*0.2476/1)
∴P ≈264.6 atm

Part 2 (ideal behavior):
we will use the ideal gas formula :
PV = nRT
when we have n = 9 
R= 0.0821
T=293 K
V= 1 L
∴P = (9*0.0821*293)/1 L
 ∴P  = 216.5 atm