science
posted by Shirley on .
A weather balloon carries instruments that measure temperature, pressure, and humidity as it rises through the atmosphere. Suppose such a balloon has a volume of 1.2 m^3 at sea level where the pressure is 1 atm and the temperature is 20°C. When the balloon is at an altitude of 11 km (36,000 ft) the pressure is down to 0.5 atm and the temperature is about – 55°C. What is the volume of the balloon then?

P*V/T is constant. That is one form of the ideal gas law when the number of moles of gas stays the same.
T must be measured in absolute degrees (K) when solving.
T1 = 293 K. T2 = 218 K
P1*V1/T1 = P2*V2/T2
Solve for V2
V2 = V1*(P1/P2)*(T2/T1)
= V1*(0.5)*(218/293)
You know V1 = 1.2 m^3, so do the numbers. 
18m^3