1. States of Matter

2. Common States of Matter
Gases
What do you know about gases?
Liquids
What do you know about liquids?
Solids
What do you know about solids?
States of matter phet

3. Kinetic Molecular Theory
The KMT relates the kinetic energy of molecules to states of matter.
Intro to KMT

4. The Nature of Gases: Kinetic Molecular Theory (KMT)
Kinetic Energy: what is it?
Energy of a moving object: Ek = ½ mv2
Assumptions of KMT as it applies to gases
Gas particles…
1. Have insignificant volume, (≈ 0)
2. Are in constant, random motion
3. Collisions are perfectly elastic
4. Do not attract or repel one another
5. Average Ek is proportional to absolute temp

5. Movement of Gas Particles in a Container

6. Gas Pressure Pressure = Force/Area:
P = F/A
Gas pressure is the result of collision of gas particles with an object.
Why is there no pressure in a vacuum?
It is the sum of the force of collisions per unit area

7. Atmospheric Pressure
Atmospheric pressure is due to the force of atmospheric gases colliding with objects and weight of atmospheric gases.

8. Barometer Measures atmospheric pressure
Invented by Alejandro Torricelli
Patm presses down on the surface, forces Hg up into the tube

9. Units of Pressure Pascal (SI unit) Pa Millimeters of Hg mmHg
Atmosphere atm
Torr torr
Conversion 25C: Know these!
1 atm = 760 mmHg = 760 torr = kPa = 14.7 psi

10. Converting Between Units of Pressure
Convert a pressure of 385 mmHg to kilopascals (kPa)
How would you do it?
51.3 kPa

11. Kinetic Energy & Temperature

12. 13.2 The Nature of Liquids
Both liquids and gases are fluids, i.e. they can flow

13. 13.2 The Nature of Liquids Key difference from gases:
Molecules are close enough to have intermolecular forces of attraction
This is why liquids have a definite volume
But not close enough to fix them in place
This is why molecules of liquids can move past one another (flow)
Condensed matter:
Liquids and solids are known as condensed phases of matter

14. Evaporation

15. Evaporation Vaporization: the conversion of a liquid to a gas or vapor
Evaporation: vaporization occurring at the surface of a liquid
During evaporation, molecules of liquid with sufficient KE “escape” in to the vapor phase
In a closed container, some molecules that escaped re-enter into the liquid phase (condense)
Eventually and equilibrium is reached where…
The rate of evaporation equals the rate of condensation
What would happen to the rate of evaporation when a liquid is heated? Why?

16. 13.2
Vapor Pressure
Vapor pressure is a measure of the force exerted by a gas above a liquid.
States of matter phet

17. Vapor Pressure
In a closed container, as molecules escape into the vapor phase, pressure builds
This is vapor pressure
At a certain pressure, the rate of vaporization equals the rate of condensation
This is an example of “dynamic equilibrium”
Then vapor pressure is constant

18. Vapor Pressure
Depends upon the liquid
Depends upon temperature

19. Vapor Pressure
Depends upon the liquid
Depends upon temperature

20. Boiling Point
A liquid boils when the particles thoughout the liquid have enough KE to vaporize
This occurs when the vapor pressure of the liquid equals the external pressure on the liquid (e.g. atmospheric pressure)
This means that a liquid can boil at different temperatures, depending on the external pressure.

21. Boiling Point & Normal Boiling Point
Normal boiling point is the boiling temperature when atmospheric pressure (Patm) = 1 atm
What is the normal BP for ethanol?
What is the BP for ethanol at Patm = 600 torr?

22. 13.3 Solids Crystal Structure Allotropes Amorphous solids Glasses
Simple cubic
Body centered cubic
Face centered cubic
Allotropes
Amorphous solids
Glasses

23. Some Types of Unit Cells

24. Allotropes Allotropes are varying forms of an element
Example: oxygen (O2) and ozone (O3)
Example: allotropes of carbon

25. Non-Crystalline Solids
Amorphous solids lack an ordered internal structure.
Examples: rubber, plastic, asphalt, glass

26. 13.4 Changes of State Vaporization/Condensation Melting/Freezing
Liquid ↔ Gas
Evaporation
Boiling
Vapor vs. Gas
Melting/Freezing
Liquid ↔ Solid
Solidification
Sublimation/Deposition
Solid ↔ Vapor
I2 (s) → I2 (g)

27. Sublimation
Solid  Vapor
Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.
Deposition
Vapor  Solid

28. Phase Diagrams
Show pressure & temperature at which various states of matter exist for a given substance
Phase equilibrium exists along each line
Normal m.p./b.p.
Triple point
Critical point
Note negative slope for solid-liquid
Unique to water

29. Phase Diagrams
A phase diagram is a graph that gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor).
Lines represent pressures and temperatures at which two phases are in equilibrium