1. Ch. 10 States of Matter Ch. 10.1 The Nature of Gases
Ch The Nature of Liquids
Ch The Nature of Solids
Ch Changes of State

2. Ch. 10.1 The Nature of Gases Kinetic theory
States that the tiny particles in all forms of matter are in constant motion
Makes 3 basic assumptions: (see pg. 267)
Gases are composed of tiny particles with very little volume and a great deal of empty space between them; no attractive forces
The particles move rapidly in random motion; they travel independently in straight paths and collisions occur
All collisions are perfectly elastic – total kinetic energy is conserved

3. Ch. 10.1 The Nature of Gases Gas pressure
Force exerted by a gas per unit surface area
Atmospheric pressure
Results from the collisions of air molecules with objects
Decreases as you move higher in the atmosphere
Barometers are used to measure atmospheric pressure (dependent on weather)
SI unit is the pascal (Pa); two older units are mm HG and atm
One standard atm is the pressure necessary to support 760mm Hg in a mercury barometer at 25oC

4. Ch. 10.1 The Nature of Gases Gas pressure
Modern barometers are aneroid
Measure the # of collisions of air molecules
It is important to measure gases under a standard condition
STP is defined as OoC and 101.3kPa or 1 atm
Kinetic energy and Kelvin temperature
When heated, particles absorb some energy as potential, the rest is kinetic and speeds up the particles
Particles have varying amounts of energy, so average kinetic energy is used
At absolute zero, 0 K, the motion of particles theoretically ceases
This has never been achieved in a lab

5. Ch. 10.2 The Nature of Liquids
A model for liquids
Particles that make up a liquid vibrate and spin as they move from place to place
this motion contributes to the kinetic energy
Most particles do not have enough energy to escape the intermolecular forces and enter the gaseous state
Liquids and solids are known as the condensed states of matter

6. Ch. 10.2 The Nature of Liquids
Evaporation
Conversion of a liquid to a gas or vapor is called vaporization
When the process occurs in a liquid that is not boiling, it is called evaporation
Liquid particles with enough kinetic energy break away from the surface and enter the gas phase
Some particles collide with air molecules and return to the liquid phase
Liquids evaporate faster when heated
Evaporation is a cooling process
When particles with high kinetic energy escape, the overall energy of the liquid is lowered

7. Ch. 10.2 The Nature of Liquids
Evaporation in a closed container has different results
Particles that escape collide with the walls if the container and produce a vapor pressure
the pressure of the gas above the liquid
Particles will continue to leave the liquid, but some will re-enter
A dynamic equilibrium exists (see pg. 276)
Rate of evaporation = rate of condensation
Increasing temperature increases the vapor pressure

8. Ch. 10.2 The Nature of Liquids
Vapor pressure can be measured with a manometer (see pg. 277)
Boiling point
The temperature at which the vapor pressure of a liquid is equal to the external pressure
Normal boiling point occurs under standard pressure
Boiling occurs more easily at high altitudes, and more slowly at low altitudes
Boiling is also a cooling process
The temperature never rises above boiling point
Liquids can only boil faster if heat increases
Vapor pressure is at the same temperature, but it has a much higher potential energy

9. Ch. 10.3 The Nature of Solids A model for solids
Particles in solids tend to vibrate about a fixed point
They are dense and incompressible
They do not flow or take the shape of their containers
Melting point
When solids are heated, the particles gain kinetic energy
Organization of the particles is disrupted
The melting point is the temperature at which a solid becomes a liquid
Disruptive vibrations overcome the strong forces holding the particles together
Melting and freezing are reverse processes (see pg. 280)

10. Ch. 10.3 The Nature of Solids Crystal structure and unit cells
Crystals have sides or faces
There are 7 types of crystal systems (see pg. 281)
The shape of a crystal depends on the arrangement of the particles
The smallest group of particles within the crystal system is called a unit cell
There are 3 types of unit cells
Some substances can take more that one crystal form – these are called allotropes

11. Ch. 10.3 The Nature of Solids Amorphous solids
Not all solids are crystalline, some are amorphous
their atoms are randomly arranged
Rubber, plastic and asphalt are amorphous solids
Glass is another type
Sometimes called supercooled liquids
Structure is intermediate between a crystalline solid and a free-flowing liquid
Does not melt, but gradually softens
Breaks in irregular shapes

12. Ch. 10.4 Changes of State Phase diagrams Sublimation
Give the conditions of temperature and pressure at which a substance exists as a solid, liquid and gas (see pg. 284)
The point at which all three curves meet is known as the triple point
Sublimation
Change of state from a solid to a gas without passing through the liquid phase
Solids have a vapor pressure
If the vapor pressure is high enough, a solid can change directly to a gas
Dry ice (solid CO2), and mothballs (naphthalene) are examples