1. Lecture Presentation
Chapter 8 Gases
Karen C. Timberlake

2. Chapter 8 Gases
Respiratory therapists assess and treat a range of patients. They perform a variety of diagnostic tests, including measuring
breathing capacity.
concentrations of oxygen and carbon dioxide in a patient’s blood, as well as blood pH.

3. Chapter 8 Readiness Key Math Skills Solving Equations (1.4D)
Core Chemistry Skills
Using Significant Figures in Calculations (2.3)
Writing Conversion Factors from Conversion Equalities (2.5)
Using Conversion Factors (2.6)
Using Molar Mass as a Conversion Factor (7.5)
Using Mole–Mole Factors (7.6)

4. 8.1 Properties of Gases
Generally molecules with fewer than five atoms from the first two periods in the periodic table are gases at room temperature. In addition, the following are also gases:
H2, N2, O2, F2, and Cl2
oxides of the nonmetals on the upper-right corner of the periodic table: CO, CO2, NO, NO2, SO2, and SO3
noble gases
Learning Goal Describe the kinetic molecular theory of gases and the units of measurement used for gases.

5. Kinetic Molecular Theory
A gas consists of small particles that
move randomly with high velocities.
have very small attractive (or repulsive) forces between molecules.
occupy a much larger volume than the volume of the molecules alone.
are in constant motion, moving rapidly in straight lines.
have a Kelvin temperature proportionate to the average kinetic energy of the molecules.
Gas particles which move in straight lines within a container, exert pressure when they collide with the walls of the container.

6. Properties That Describe a Gas
Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and amount (n).

7. Volume The volume of a gas
is the same as the volume of the container it occupies.
is usually measured in liters or milliliters.
increases with an increase in temperature at a constant pressure.
Gas particles which move in straight lines within a container, exert pressure when they collide with the walls of the container.

8. Temperature
The temperature of a gas relates to the average kinetic energy of the molecules and is measured in the Kelvin (K) temperature scale.
When the temperature of a gas is
decreased, the molecules have fewer collisions.
increased, the molecules have more collisions.

9. Pressure
Pressure is a measure of the gas particle collisions with sides of a container and is measured in units of
millimeters of mercury, mmHg or torr.
atmospheres, atm.
pascals, Pa, or kilopascals, kPa.
pounds per square inch, psi.
Gas particles in the air exert pressure on us called atmospheric pressure.

10. Barometers Measure Pressure
A barometer
measures the pressure exerted by the gases in the atmosphere.
indicates atmospheric pressure as the height in mm of the mercury column.
760 mmHg = 1 atm = 760 Torr
The barometer was invented by Evangelista Torricelli, at exactly 1 atm the barometer tube measures exactly 760 mm high.

11. Units of Pressure

12. Atmospheric Pressure
Atmospheric pressure
is the pressure exerted by a column of air from the top of the atmosphere to the surface of Earth.
decreases as altitude increases.
about 1 atm at sea level.

13. Altitude and Atmospheric Pressure
Atmospheric pressure changes with variations in weather and altitude.
On a hot, sunny day, the mercury column rises, indicating a higher atmospheric pressure.
On a rainy day, the atmosphere exerts less pressure, which causes the mercury column to fall.

14. Study Check What is 475 mmHg expressed in atm? 475 atm 0.625 atm
2. The pressure in a tire is 2.00 atm. What is this pressure in mmHg?
2.00 mmHg
1520 mmHg
mmHg

15. Solution What is 475 mmHg expressed in atm?
The answer is B, atm.
The pressure in a tire is 2.00 atm. What is this pressure in mmHg?
The answer is B, 1520 mmHg. × ×

16. Study Check
The downward pressure on the Hg in a barometer is _____ the pressure of the atmosphere.
A. greater than B. less than C. the same as
A water barometer is 13.6 times taller than an Hg barometer (dHg = 13.6 g/mL) because
A. H2O is less dense than mercury.
B. H2O is heavier than mercury.
C. air is more dense than H2O.

17. Solution
The downward pressure on the Hg in a barometer is _____ the pressure of the atmosphere. The answer is C, the same as.
A water barometer is 13.6 times taller than an Hg barometer (dHg = 13.6 g/mL) because The answer is A, H2O is less dense than mercury.