1. Physical Characteristics of Gases
Pressure

2. Objectives Define pressure and relate it to force
Describe how pressure is measured.
Convert units of pressure.
State the standard conditions of temperature and pressure.

3. Pressure To adequately describe a gas, you must know… Volume
Temperature
Number of particles
Pressure

5. Atmospheric Pressure
The gases that make up the atmosphere exert pressure on their surroundings. It is a result of:
Collisions between gas particles.
The weight of the atmospheric gases above the earth’s surface.

6. Measuring Pressure Atmospheric pressure is measured using a barometer.
Atmospheric pressure depends on elevation and weather.
Normal atmospheric pressure at sea level: 760 mm Hg

8. Measuring Pressure
A manometer can be used to measure the pressure of an enclosed gas.
The pressure is measured relative to atmospheric pressure.

9. Std. Atmospheric pressure
Units of Pressure
Unit
Symbol
Std. Atmospheric pressure
Millimeters of Hg
mm Hg
760
Centimeters of Hg
cm Hg 76
Inches of Hg
in. Hg
29.92
Torr
Pascals (N/m2) Pa
101,325
Atmospheres
atm 1
Pounds per square inch
psi
14.69
bars
bar
The Pascal is the SI unit

10. Pressure Conversions
Convert 35 psi into units of atmospheres.

11. Standard Temperature and Pressure
Conditions used by scientists for comparison.
1 atm
0oC