Ch5 Lec 1

Solutions Review...watch this "Crash Course" video (don't worry about taking notes).

Chapter 5: Gases

Section 5.1: Substances that exist as gases

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Take home points:

- Air is 78% N₂, 21% O₂, 1 % other

- Many elements exists as gases, H₂, N₂, O₂, halogens and the noble gases.

- There are other molecular substances that exist as gases, HCl, CO, CO₂, NH₃ (ammonia), CH₄ (methane), NO₂, SO₂, H₂S.

- Gases:

- fill the volume of space that exist in,

- are compressible,

- when 2 gases are mixed, they will mix together to make a homogenous mixture,

- have a density (g/mL), but much lower than a solid or liquid.

Section 5.2: Pressure of a gas

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Additional comments:

You do not often acknowledge the fact that you currently have a column of gas/air sitting on the top of your head. This column of air exerts a pressure (a force per area) on your head and shoulders. Now this amount of pressure exerted by air is quite smaller compared to the pressure exerted on your hips and knees by your upper body mass, but none the less the column of air above you exerts pressure. This is an interesting demo that i sometime do in class:

https://www.youtube.com/watch?v=UvMmfacVA24

Units of gas pressure

The most common gas pressure unit is a Pascal (Pa), but most of you are more familiar with an "atmosphere" (atm). A Pa is equal to 1 Newton of force/1 square meter. The column of air stilling on top of your head right now is exerting ~ 1 atm or 101,325 Pa. Apparently a Pa is a very small unit, so we often think about kiloPascals (kPa) and not Pa.

1 atm = ~ 101 kPa

Section 5.6: Dalton's law of partial pressures

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