Please help me, I can't figure this out. You have a 450.0 mL balloon filled with 0.0184 moles of Helium gas. The volume of the balloon will change, but the pressure of the gas inside will always match the 1.00 atm pressure outside. If the balloon is kept at a constant 25oC, how many moles of gas must you remove to shrink the balloon down to 200.0 mL?