# Gases

## CHM 101

https://youtu.be/PWWIiVNhfaA
https://youtu.be/H1n_zo-Maz0
Lecture and practice problems on ideal gas law and gas stoichiometry. You can skip the section on gas stoichiometry-forward to the practice problems: 1-4.

## Pressure-A gas thing!

Pressure affects gases much more than in solids or liquids. Gases are compressible and, therefore, the pressure on a gas can be increased. Pressure of gases comes from the collision of the gas particles with any surface (including the earth's surface!) so the more of them you have, the more pressure. The faster the gas particles are moving (higher temperatures), the more often they will collide with a surface, and therefore, the higher the pressure. Because the motion of gas particles is so much greater than in liquids and solids, there are more collisions with the container than in solids or liquids. Pressure is measured via many different units. Converting between the different units for pressure is a necessary evil for chemistry students.

STP or standard temperature and pressure is useful because we can compare volumes of gases if we have a standard temperature and pressure for comparison. The standard temperature is 0 ºC or 273.15 K and standard pressure is exactly 1 atm (same as 760 mm Hg or 760 torr or 101,325 Pa or 14.7 psi or 29.92 in Hg).

Boyle's Law Science Lab
MIT Physics Demo -- Balloons in Liquid Nitrogen
https://youtu.be/xg5NiOwf_Zw

## Dalton's Law

Dalton's Law of Partial Pressures states that the total pressure, Ptotal, of a mixture of gases is equal to the sum of the partial pressures of the gases making up the mixture. Notice the word "mixture", this law does not apply to cases where the gases react in a chemical reaction. The air we live in would apply to Dalton's Law. Because our air especially contains a lot of water here in the gulf south, the water vapor in the air is also a part of this gas mixture. We call this partial pressure of water vapor, the vapor pressure of water and, like all gases, that pressure is dependent on the same factors affecting gases like V, amount and especially T. Which season has more water vapor in the air: summer or winter?.