1. Basic Chemistry Chapter 11 Gases Chapter 11 Lecture 11.2 Gas Pressure
Fourth Edition
Chapter Gases
11.2 Gas Pressure
Learning Goal Describe the units of measurement used for pressure, and change from one unit to another.

2. Gas Pressure
When billions of gas particles collide with the walls of a container, they exert pressure, which is defined as force acting on a certain area.

3. Atmospheric Pressure
Atmospheric pressure can be measured using a barometer.

4. Measuring Gas Pressure, Units
One atmosphere (atm) is defined as exactly 760 mmHg.
1 atm = 760 mmHg = 760 torr (exact)
1 mmHg = 1 torr (exact)
In SI units, pressure is measured in pascals (Pa);
1 atm = × 105 Pa = kPa

5. Measuring Gas Pressure, Units

6. Altitude and Atmospheric Pressure
Atmospheric pressure changes with altitude and weather.
Location
Altitude
(km)
Atmospheric Pressure (mmHg)
Sea Level
0.00
760
Los Angeles
0.09
752
Mount Whitney
4.50
440
The atmospheric pressure decreases as the altitude increases.

7. Learning Check
What is 475 mmHg expressed in atm?
A. 475 atm
B atm
C × 105 atm

8. Solution
What is 475 mmHg expressed in atm?
0.625 atm

9. Learning Check
The pressure in a tire is 2.00 atm. What is this pressure in mmHg?
A mmHg
B mmHg
C mmHg

10. Solution
The pressure in a tire is 2.00 atm. What is this pressure in mmHg?
1520 mmHg