When filling a weather balloon with gas you have to consider that the gas will expand greatly as it rises and the pressure decreases. Let’s say you put about 9.00 moles of He gas into a balloon that can inflate to hold 3000.0 L. Currently, the balloon is not full because of the high pressure on the ground. What is the pressure when the balloon rises to a point where the temperature is -15.°C and the balloon has completely filled with the gas.