602 The Kinetic Theory of GasesQ21.10The dry air is more dense. Since the air and the water vapor are at the same temperature, they havethe same kinetic energy per molecule. For a controlled experiment, the humid and dry air are at thesame pressure, so the number of molecules per unit volume must be the same for both. The watermolecule has a smaller molecular mass (18.0 u) than any of the gases that make up the air, so thehumid air must have the smaller mass per unit volume.Q21.11Suppose the balloon rises into air uniform in temperature. The air cannot be uniform in pressurebecause the lower layers support the weight of all the air above them. The rubber in a typical balloonis easy to stretch and stretches or contracts until interior and exterior pressures are nearly equal. Soas the balloon rises it expands. This is an isothermal expansion, with Pdecreasing as Vincreases bythe same factor in PVnRT=. If the rubber wall is very strong it will eventually contain the helium athigher pressure than the air outside but at the same density, so that the balloon will stop rising.
This is the end of the preview.
access the rest of the document.
As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.
Temple University Fox School of Business ‘17, Course Hero Intern
I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.
University of Pennsylvania ‘17, Course Hero Intern
The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.