Ahelium balloon is filled to a volume of 2.88 x 103 l at 722 mm hg and 19â°c. when the balloon is released, it rises to an altitude where the pressure and temperature are 339 mm hg and -55oc, respectively. what is the volume of the balloon (in l)

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.