Example. An eight-foot diameter weather balloon is filled with 7600 liters of hydrogen gas at sea level where the pressure is 1 atm. By the time the balloon has ascended to an altitude at which the pressure is 0.70 atm, what is the volume of the balloon?

Solution 1. Use Boyle's law in the form PV = k and evaluate k. At sea level,
P = 1 atm, and V = 7600 liters; thus

k = PV = (1 atm) (7600 liters) = 7600 liter atm.

This constant is equally valid for any other P and V, as long as the temperature is unchanged. (This is a flaw in our example. The temperature actually would change with altitude.) We can then write

(0.70 atm) V = 7600 liter atm