1. Introductory Chemistry, 3rd Edition Nivaldo Tro
Chapter 11
Gases

2.
Tro's Introductory Chemistry, Chapter 11

3. Properties of Gases Expand to completely fill their container.
Take the shape of their container.
Low density.
Much less than solid or liquid state.
Compressible.
Mixtures of gases are always homogeneous.
Fluid.
Tro's Introductory Chemistry, Chapter 11

4. The Structure of a Gas
Gases are composed of particles that are flying around very fast in their container(s)
They move in straight lines until they encounter something
Particles in a gas, you would find that there is a lot of empty space
Tro's Introductory Chemistry, Chapter 11

5. Kinetic Molecular Theory
Particles (either atoms or molecules) are constantly moving
The attraction between particles is negligible
When the moving particles hit another particle or the container, they do not stick, but they bounce off and continue moving in another direction.
Like billiard balls.
Tro's Introductory Chemistry, Chapter 11

6. Kinetic Molecular Theory of Gases
There is a lot of empty space between the particles in a gas.
Compared to the size of the particles.
The average kinetic energy of the particles is directly proportional to the Kelvin temperature.
As you raise the temperature of the gas, the average speed of the particles increases.
But don’t be fooled into thinking all the particles are moving at the same speed!!
Tro's Introductory Chemistry, Chapter 11

7. Kinetic Molecular Theory
Tro's Introductory Chemistry, Chapter 11

8. Gas Particles Pushing Gas molecules are constantly in motion
As they move and strike a surface, they push on that surface.
Push = force.
If we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exerting.
Pressure = force per unit area.
Tro's Introductory Chemistry, Chapter 11

9. The Effect of Gas Pressure
The pressure exerted by a gas can cause some amazing and startling effects.
Whenever there is a pressure difference, a gas will flow from area of high pressure to low pressure.
The bigger the difference in pressure, the stronger the flow of the gas.
If there is something in the gas’ path, the gas will try to push it along as the gas flows.
Tro's Introductory Chemistry, Chapter 11

10. Gas Properties Explained
Gases have taken the shape and volume of their container(s)
In solids and liquids, the particles are attracted to each other strongly enough so they stick together.
Gases are compressible and have low density because of the large amount of unoccupied space between the particles.
Tro's Introductory Chemistry, Chapter 11

11. Properties—Indefinite Shape and Indefinite Volume
Because the gas
molecules have
enough kinetic
energy to overcome
attractions, they
keep moving around
and spreading out
until they fill the
container.
As a result, gases
take the shape and
the volume of the
container they
are in.
Tro's Introductory Chemistry, Chapter 11

12. Properties—Compressibility
Because there is a lot of unoccupied space in the structure
of a gas, the gas molecules can be squeezed closer together.
Tro's Introductory Chemistry, Chapter 11

13. Gas Properties Explained— Low Density
Because there is a lot of unoccupied space in the structure of a gas, gases do not have a lot of mass in a given volume, the result is that they have low density.
Tro's Introductory Chemistry, Chapter 11

14. The Pressure of a Gas
Pressure is the result of the constant movement of the gas molecules and their collisions with the surfaces around them.
The pressure of a gas depends on several factors:
Number of gas particles in a given volume.
Volume of the container.
Average speed of the gas particles.
Tro's Introductory Chemistry, Chapter 11

15. Density and Pressure
Pressure is the result of the constant movement of the gas molecules and their collisions with the surfaces around them.
When more molecules are added, more molecules hit the container at any one instant, resulting in higher pressure.
Also higher density.
Tro's Introductory Chemistry, Chapter 11

16. Air Pressure
The atmosphere exerts a pressure on everything it contacts.
On average 14.7 psi.
The atmosphere goes up about 370 miles, but 80% is in the first 10 miles from Earth’s surface.
This is the same pressure that a column of water would exert if it were about 10.3 m high.
Tro's Introductory Chemistry, Chapter 11

17. Measuring Air Pressure
Use a barometer.
Column of mercury supported by air pressure.
Force of the air on the surface of the mercury balanced by the pull of gravity on the column of mercury.
gravity
Tro's Introductory Chemistry, Chapter 11

18. Atmospheric Pressure and Altitude
The higher up in the atmosphere you go, the lower the atmospheric pressure is around you.
At the surface, the atmospheric pressure is 14.7 psi, but at 10,000 ft is is only 10.0 psi.
Tro's Introductory Chemistry, Chapter 11

19. Common Units of Pressure
Average air pressure at sea level
Pascal (Pa)
101,325
Kilopascal (kPa)
Atmosphere (atm)
1 (exactly)
Millimeters of mercury (mmHg)
760 (exactly)
Inches of mercury (inHg)
29.92
Torr (torr)
Pounds per square inch (psi, lbs./in2)
14.7
Tro's Introductory Chemistry, Chapter 11

20. Convert 45.5 psi into kPa.
Tro's Introductory Chemistry, Chapter 11