I am stuck on this now....As a birthday balloon is filled with helium, the amount of helium increases from 0.5 moles of helium to 5.5 moles of helium. If the initial volume of the balloon is 2.5 mL, what is the final volume?

Answer 1

P V = n R T
T is constant
assume P is pretty constant, room pressure. Inside balloon is not much higher than outside because material is very weak.
V = (R T/P) n where (RT/P) is constant
so V2 / n2 = V1 / n1
V2/ 5.5 = 2.5 / 0.5
V2 = 2 (2.5 * 5.5) mL
so what is 5 * 5.5 :) ?