1. States of Matter

2. Kinetic Theory The word “Kinetic” refers to motion
The energy an object has because of it’s motion is called kinetic energy
The kinetic theory states that the tiny particles in all forms of matter are in constant motion!

3. Kinetic Theory & Gases Assumption #1:
Three basic assumptions of the kinetic theory as it applies to gases:
Assumption #1:
Gas is composed of particles-
usually molecules or atoms
Behave as small, hard spheres
Each particle has insignificant volume;
relatively far apart from each
other (when compared to solids or liquids)
No attraction or repulsion between particles (particles are more free to move around more than in a liquid)

4. Kinetic Theory & Gases Assumption #2: Particles in a gas move
rapidly in constant random
motion
Move in straight paths,
changing direction only
when colliding with one
another or other objects
Average speed of O2 in air at 20 oC is an amazing 1700 km/h! (1056 mph)

5. - Page 385

6. Kinetic Theory & Gases Assumption #3:
When gas particles collide, no energy is lost.
What this means:
When large objects (like cars) collide some of the kinetic energy is changed into other forms of energy (such as heat from friction)
Before
After
ECar1 = 10
ECar2 = 10
ECar1 + ECar2 = 15
Ecar1 + ECar2 = 20
+ thermal energy (heat) = 5

7. Kinetic Theory & Gases
When particles collide kinetic energy is transferred from one particle to another- the total kinetic energy of the system remains constant
When gas particles collide, no energy is lost…this is a perfectly elastic collision
After
Before
Eatom = 10
Eatom = 10
Eatom + Eatom = 20
Eatom + Eatom = 20

8. Studying the Behavior of Gases
Focus on three things:
Volume: how much space a gas takes up
Pressure
Temperature

9. Gas Pressure
Gas Pressure is defined as the force exerted by a gas per unit surface area of an object

10. Gas Pressure
Less collisions
Gas exerts pressure because moving particles exert a force when they collide
The greater that force, the greater the pressure
The greater the number of collisions, the greater the pressure
No particles present?
Then there cannot be any collisions, and thus no pressure – called a vacuum
More collisions
Vacuum

11. Measuring Gas Pressure
The SI unit of pressure is the pascal (Pa)
Older units of pressure: millimeters of mercury (mm Hg), and atmospheres (atm)
Atmospheric pressure: pressure exerted on objects due to the gas particles in the atmosphere.
Results from the collisions of air molecules with objects
Decreases as you climb a mountain because the air “thins” as elevation increases
air density decreases

12. Barometer measuring device for atmospheric pressure
An Early Barometer
measuring device for atmospheric pressure
which is dependent upon weather & altitude
Mercury Barometer – a straight glass tube filled with Hg, and closed at one end; placed in a dish of Hg, with the open end below the surface

13. Standard Pressure 1 atm = 760 mm Hg = 101.3 kPa
An Early Barometer
The normal pressure due to the atmosphere at sea level (25oC) can support a column of mercury that is 760 mm high.
We call this 1 atmosphere of pressure.
1 atm = 760 mm Hg = kPa

14. Standard Temperature and Pressure
Especially for gases, it is important to relate measured values to a standard.
This gives us a frame of reference.
Standard Temperature and Pressure, or STP
--Standard conditions are defined as a temperature of 0 oC and a pressure of kPa, or 1 atm
Normal boiling point- is defined as the boiling point of a liquid at a pressure of kPa (or standard pressure) Normal freezing point, Normal melting point, etc.

15. Temperature so, temperature increases
What happens when you add heat (thermal energy)
to a substance?
First, particles absorb energy – NO temperature change
Some of the energy is stored within the particles as potential energy, and does not raise the temperature
Second, temperature increases
When the particles cannot store any more energy, additional thermal energy will cause the particles to speed up
Average kinetic energy increases
so, temperature increases

16. Water temp. increases 24oC Olive oil temp. increases 50oC
How does this happen?
Heat and Temperature are not the same thing:
Heat is thermal energy,
temperature is a measure of the average kinetic energy in molecules
Why?
The particles in water can store more potential energy
Less thermal energy (heat) left over to raise temperature
Remember – Water has high specific heat!
These are liquids, but gases work the same way.
10g olive oil
10g pure water
J heat
J heat
Water temp. increases 24oC
Olive oil temp. increases 50oC

17. Average KE & Kelvin Scale
The Kelvin temperature scale reflects a direct relationship between temperature and average kinetic energy
Particles of a gas at 200 K have twice the average kinetic energy as particles of a gas at 100 K
What happens here?
When Temperature Kelvin = 0, does kinetic energy reach 0?
Doesn’t 0 kinetic energy mean 0 motion?
ABSOLUTE ZERO
Temp. Kelvin
Average Kinetic Energy

18. The Nature of Liquids Liquid particles are also in motion.
Gases and liquids can both FLOW
However, liquid particles are attracted to each other, whereas gases are not
Intermolecular attractions reduce the amount of space between particles of a liquid. So, liquids are denser than gases (except H2O)
Increasing pressure on liquid has hardly any effect on it’s volume

19. KE of Liquid Particles
most of the particles do not have enough energy to escape into the gaseous state;
they would have to overcome their intermolecular attractions with other particles
Remember: water has hydrogen bonds!

20. Phase Change (Liquid -> Gas)
Vaporization - The conversion of a liquid to a gas or vapor.
Vaporization can occur in a liquid that is NOT boiling
Vaporization can occur in a liquid that IS boiling

21. 1. Evaporation
Evaporation - vaporization occurs in a liquid that is not boiling.
Evaporation occurs at the surface of the liquid
Some of the particles have more kinetic energy (KE) than others.
The particles with enough KE to overcome intermolecular forces break away and enter the gas or vapor state

22. Effect of Liquid Temperature on Evaporation
When you raise a liquid’s temperature by adding heat, the average kinetic energy of the particles is increased which means more liquid particles are likely to have enough kinetic energy to overcome attractive forces between particles (like hydrogen bonds) to become gas particles. So, liquids with higher temperatures will evaporate faster.
Particles left behind in liquid are the ones with lower average kinetic energies; they didn’t have enough energy to escape.
evaporative cooling - Evaporation is often called a cooling process. On a hot day we sweat to keep cool.

23. What if the liquid is in a closed container?
When some particles do vaporize, these
collide with the walls of the container
producing vapor pressure
Some of the particles will return to the liquid, or condense
After a while, the number of particles evaporating will equal the number condensing- the space above the liquid is now saturated with vapor
A dynamic equilibrium exists
Rate of evaporation = rate of condensation
Increasing the temperature increases the KE of the particles  increases the vapor pressure

24. 2. Vaporization of a Boiling Liquid
The rate of evaporation from an open container increases as heat is added
The heating allows larger numbers of particles at the liquid’s surface to overcome the attractive forces
Heating allows the average kinetic energy of all particles to increase

25. Boiling a Liquid The temperature at which a liquid will boil
is called its boiling point (bp).
Particles beneath the surface have enough energy to overcome their attractive forces.
Gas bubbles form below the surface.
At boiling, the vapor pressure of the liquid is just equal to the external pressure on the liquid (atmospheric pressure in an open container)
Supplying more heat allows particles to acquire enough KE to escape- the temperature does not go above the boiling point, the liquid only boils at a faster rate

26. Effect of Pressure on Boiling Point
Montrose: Normal bp of water = 100 oC
Denver: Normal bp of water = 95 oC,
Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kPa
How pressure cookers work:
Sealed container allows pressure to increase beyond atmospheric pressure
Higher pressure  higher boiling point
The temperature rises above 100 oC and food cooks faster.

27. - Page 394
Normal Boiling kPa = 100 oC
Not Boiling
Boiling, 34 kPa = 70 oC

28. Questions:

29. The Nature of Solids
Most solids have particles packed against one another in a highly organized pattern
Tend to be dense and incompressible
Do not flow, nor take the shape of their container
Are still able to move, vibrating about fixed points, rather than moving from place to place
(unless they reach absolute zero)
Images from

30. Heating Solids
When a solid is heated, kinetic energy of the particles increases.
More kinetic energy means the particles vibrate more rapidly and more vigorously
As a result, solids tend to expand when heated

31. Phase Change (Solid-> Liquid)
If enough heat is added to a solid
and the kinetic energy becomes
high enough – a solid will melt.
The melting point (mp) is the temperature
at which a solid turns to a liquid
At the melting point, the particle vibrations are strong enough to overcome the interactions holding them in a fixed position
Melting can be reversed by cooling the liquid so it freezes
Solid liquid

32. Melting Points of Solids
Ionic Compounds and Network Solids:
Generally, have high melting points, due to the relatively strong forces holding them together
Sodium chloride (an ionic compound) has a melting point = 801 oC
Molecular Compounds:
Generally, have relatively low melting points because their intermolecular forces are weaker (ex: Vander waals or dipole forces)

33. Microscopic Structure of Solids
Most solid substances are crystalline in structure.
In a crystal, the particles (atoms, ions, or molecules) are arranged in a orderly, repeating, three-dimensional pattern called a crystal lattice (All crystals have a regular shape, which reflects their arrangement)

34. Carbon Solids
Carbon is a good example of the significance the crystal structure plays in the compound characteristics.
Allotropes are two or
more different molecular
forms of the same
element in the same physical state like carbon.
Diamond, Graphite, Buckminsterfullerene are three different substances formed from pure carbon.
Differences in how the C atoms bond to each determine the crystal structure and the substance properties.

35. Phase Change
Sublimation- the change of a substance from a solid directly to a vapor, without passing through the liquid state. (solid -> gas)
Examples:
iodine
dry ice (-78 oC);
mothballs;
solid air fresheners
Deposition-the change of a substance from a vapor directly to a solid, without passing through the liquid state (gas -> solid)

36. Changes of State