Use Boyle’s law P1V1 = P2V2
Rearrange equation to solve for V2
(P1 x V2)/P2 = V2
P1 = 2 atm
V1 = 1L
P2 = 400 kpa (convert to atm by dividing by 101) —> 3.94 atm
Substitute in equation:
(2 x 1)/3.94 = 0.5 L (rounded)
Scientifically this makes sense because Boyle’s law states that Pressure and Volume are inversely proportional so when one increases the other decreases. In this case the pressure is almost doubled, so the volume is halved.