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.