1. Pressure

2. 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 = 101.3 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. There are 3 major temperature scales Fahrenheit, Celsius, Kelvin All 3 scales are related K = o C + 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 = -273 o C = ⓪K

10. Standard Temperature and Pressure (STP) Standard temperature = 0 o 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 50 o C to Kelvin.