Example. An eight-foot diameter weather balloon is filled with 7600 liters of gas at 1 atm. pressure and 25. As the balloon rises to an altitude where the pressure is only 0.70 atm, the temperature drops to -20. What then is the volume of the balloon?

Solution. Let sea-level conditions be denoted by subscript 1, and high altitude conditions, by 2. The number of moles of gas does not change, so we can use the ideal gas law in the form


or









The decrease in pressure to 0.70 atm causes an increase in volume by a factor of 1.00/0.70, but the simultaneous drop in temperature causes a shrinkage by a factor of 253/298. The balloon does not expand as much as it would have if the temperature had remained constant.