1. Gas Laws
Pressure

2. Pressure The amount of force an object puts on a surface.
Pressure is measured by a barometer.
Atmospheric pressure comes from air being pulled down by gravity.
Atmospheric pressure changes with altitude – higher elevations have lower atmospheric pressure.

3. Units of pressure
There are a few units of pressure that we use in chemistry.
kPa = kilopascal
atm = atmosphere
Mm Hg = millimeters of mercury
Torr
Psi = pounds per square inch

4. Pressure conversions
All these units are different ways of measuring the same thing.
We can convert from one unit to another using the following relationship:
1 atm = 760 mm Hg = 760 Torr = kPa = 14.7 psi
This relationship allows us to make conversion factors between units of pressure.

5. Examples
1. Convert the pressure of a gas from 2 atm to mm Hg. 2. Convert the pressure of a gas from 29.4 psi to atm.

6. 3. Convert 1520 mm Hg to kPa.

7. Temperature The measure of the kinetic energy of particles.
The higher the temperature, the more energy the particles have.
Raising the temperature of a gas will also increase the pressure of the gas.
Pressure is caused by the collisions of the gas particles with the walls of their container.
As a gas is cooled, it will compress, or shrink, and the pressure will decrease.
If you blow up a balloon and place it in the freezer, it will shrink.

8. Temperature scales There are 3 major temperature scales
Fahrenheit, Celsius, Kelvin
All 3 scales are related
K = oC + 273
o F = o C(1.80) + 32

9. Absolute zero The lowest possible temperature that exists.
At this temperature, all molecular motion stops.
Absolute zero = -273o C = ⓪K

10. Standard Temperature and Pressure (STP)
Standard temperature = 0o C
Standard Pressure = 1 atm
At STP, all gases have a volume of 22.4 L, called molar volume.

11. Temperature Conversions
Convert 50 K to degrees Celsius.
Convert 50o C to Kelvin.