Throughout this course we've been talking about how gas is a bunch of bouncy little balls that go crashing into each other. I call it a mosh pit, the official name is Kinetic-Molecular theory, but both describe a situation which is the basis of all the gas laws to follow.
Units of Pressure, Volume & Density
This video explains what pressure is and how to calculate it, and it explains why "millimeters mercury" is a reasonable unit of pressure. We'll also cover how to convert between all the crazy units of pressure, including torr, mm Hg, Pascals (Pa), kPa, psi, and atmospheres (atm).
Molar Volume & Density
This video is for a very specific type of problem which some teachers use, which takes advantage of the fact that at STP, one mole of any gas will occupy 22.4 liters. This is a good skill to have, even if your teacher doesn't put "molar density" in the syllabus.
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)