How do I solve this problem, they are killing me

Question

Hey 1.2 L weather balloon on the ground has a temperature of 25 Celsius and atmospheric Pressure 1.0 ATM. When it rises to elevation where the pressure is 0.72 Atm, then the new volume is 1.8 L. What is the temperature in Celsius of the air at this elevation.

Answer 1

Use the ideal gas law which is PV = nRT where P is in atmospheres, V is in liters, and T is absolute temperature (25C + 273). You can then calculate nR which is the gas constant times the number of moles of gas. The ideal gas equation can be used again with P = 0.72, V = 1.8L, and the value of nR calculated above. Solve the equation for T and subtract 273 to get the temperature in degrees Celsius. I got t = 51 ºC.