1. The Nature of Gases Kinetic Energy – the energy an object has because
of its motion.
Kinetic – means motion
Kinetic Theory – all matter consists of tiny particles that are in constant motion.

2. Kinetic Theory
Kinetic theory says that molecules are in constant motion.
Perfume molecules moving across the room are evidence of this.

3. The Kinetic Theory of Gases Makes three descriptions of gas particles
A gas is composed of particles
molecules or atoms
Considered to be hard spheres far enough apart that we can ignore their volume.
Between the molecules is empty space.

4. The particles are in constant random motion.
Move in straight lines until they bounce off each other or the walls.
All collisions are perfectly elastic

5. The Average speed of an oxygen molecule is 1656 km/hr at 20ºC
The molecules don’t travel very far without hitting each other so they move in random directions.

6. Pressure
Pressure is the result of collisions of the molecules with the sides of a container.
A vacuum is completely empty space - it has no pressure.
Pressure is measured in units of atmospheres (atm).
It is measured with a device called a barometer.

7. Barometer At one atmosphere pressure a column of mercury 760 mm high.
1 atm Pressure
Column of Mercury
Dish of Mercury

8. Barometer At one atmosphere pressure a column of mercury 760 mm high.
A second unit of pressure is mm Hg
1 atm = 760 mm Hg
Third unit is the Pascal
1 atm = kPa
1 atm Pressure
760 mm

9. Pressure units Convert kilopascals – kPa 1 atm = 760 mm Hg = 101.3 kPa
743 mm Hg to atm
895 kPa to mm Hg

10. Gas Pressure
Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.
e.g. – a helium-filled balloon maintains its shape because of the pressure of the gas within it.
Vacuum – an empty space with no particles and no pressure. (no particles, no collisions)

11. Atmospheric Pressure
Atmospheric pressure results from the collisions of atoms and molecules in air with objects.
Atmospheric pressure decreases as you climb
a mountain because the density of Earth’s atmosphere decreases as elevation increases.
less particles, less pressure

12. The Nature of Liquids Particles are in motion.
Tends to pull them apart
Attractive forces between molecules keep them close together.
liquids are much more dense than gases.
These are called intermolecular forces.
Inter = between

13. Vaporization - the change from a liquid to a gas below its boiling point.
Evaporation - vaporization of an uncontained liquid ( no lid on the bottle ).

14. Evaporation Molecules at the surface break away and become gas.
Only those with enough KE escape
It requires energy.

15. Solids Intermolecular forces are strong Molecules still move
Can only vibrate and revolve in place.
Particles are locked in place - don’t flow.
Melting point is the temperature where a solid turns into a liquid.
The melting point is the same as the freezing point.

16. Phase Changes Solid Gas Liquid Melting Vaporization Freezing
Condensation

17. Sublimation
Sublimation – the change of a substance from a solid to a vapor without passing through the liquid state.
Sublimation can occur because solids, like liquids, have vapor pressure.
Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.

18. For example:
Solid carbon dioxide (dry ice) sublimes at atmospheric pressure.
Used as a coolant. It does not produce a liquid as ordinary ice does when it melts.

19. Solid Gas Liquid Require energy Sublimation Melting Vaporization
Deposition
Freezing
Condensation
Release energy

20. End of Chapter 13