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

Since the balloon is expandable, as you add more helium, the volume will increase in order to keep the pressure constant. If it didn't expand, the pressure would increase and the balloon would burst. Also, it is assumed that the temperature remains constant as nothing in the problem indicates otherwise.

Thus, we are faced with an issue where the volume increases as a function of the number of moles of He.

From the ideal gas law, PV = nRT, we see that if the pressure (P) and the temperature (T) are both constant, as is R (the gas constant), we are left with V = kn where k is another constant. Or, Volume is directly proportional to moles.

0.5 moles/2.5 ml = 5.5 moles/x mls

x = 27.5 mls

The moles increased from 0.5 to 5.5 which is 11 times, so the volume should increase 11 times.

2.5 mls x 11 = 27.5 mls