1. Chapter 7
Matter

2. Objectives Define Density
Define pressure and calculate the pressure of a fluid
Use the kinetic model to describe the structures of solids, liquids, and gases and to explain changes of state and the pressure of a gas

3. Density Density is a macroscopic property of matter
Macro = large scale
It tells us about how concentrated the matter is
Density is a constant for a given material
Density = mass/volume
Ρ (Greek letter rho)= m/V

4. Density continued SI unit for density is kg m-3
can also be quoted in g cm-3
Density of water is approximately 1000 kg m-3

5. Pressure
Pressure tells you about how the force is shared out over the area it acts on
Pressure is defined as the normal force acting per unit cross-sectional area.
Pressure = normal force/cross sectional area
p= F/A
Pressure unit are Newtons per square meter, which are called pascals
1 Pa = 1 N m-2

6. Pressure in a fluid Pressure in fluid increases with depth
Decreases with height
Pressure is due to the weight of the atmosphere above us, pressing down, when pulled by gravity

7. Pressure of a fluid Depends on three variables
The depth h below the surface
The density of the fluid ρ
The acceleration due to gravity g
p= ρgh
Pressure = density x acceleration x depth

8. Pressure of a fluid Volume of water = A h
Mass of water = density x volume = ρ A h
weight of water = mass x g = ρ A h g
Pressure = Force /area = ρ A h g/A
= ρ g h

9. Kinetic Model
Used to describe matter and explain its properties and behavior, based on these assumptions
Matter is made up of tiny particles
These particles tend to move about
For simplicity, matter refers to atoms

10. Three states of matter
Describe the differences between each state based on three criteria
The spacing of the atoms – how far apart?
The ordering of the atoms – order or random
Motion of the atoms – moving quickly or slowly

11. Order and Disorder
Solids are classified to how the molecules are arranged
Crystalline solid –particles are arranged in a regular pattern – like metals or crystals (duh)
Amorphous – particles are arranged in a random way (glass)
Polymer - a solids made up of long molecules, and cross links with other chains (rubber), can deform under force and return to original shape

12. Atoms of a Gas We picture the atoms of a gas as fast moving
They moved about in a disordered way
Scottish botanist, Robert Brown provided direct evidence of air molecules
Brownian motion describes the jerky and erratic path that a single particle travels in a gas

13. Atoms of gas
Since air molecules are much smaller than smoke grains, it can be determined that the air molecules are traveling much faster
Brownian motion can also be explained in liquids as well

14. Fast Molecules
Air molecules average speed is 400 ms-1 at standard temperature and pressure (STP = 0oC and 100kPA)
Velocity and direction are constantly changes every time it collides with anything else.
Air molecules move faster than the speed of sound (330 ms-1 at STP).
Faster molecules can escape Earth’s gravitational pull (more than 11Km s-1), why we have an atmosphere.

15. Explaining Pressure
A gas exerts pressure on any surface with which it comes into contact.
Pressure is a macroscopic property
Force of air pressure by the atmosphere acting on a person is about N.
Since our internal pressure is equal to our external pressure, we don’t collapse under the force

16. Pressure continued
When air molecules are colliding with in inside of a container, they exert a small amount of force on the container,
Two factors affect the force and therefor the pressure, that a gas exerts on a the box
The number of molecules that hit each side of the box in one second
The force with which one molecule collides with the wall.

17. Pressure continued still…
The higher the pressure of a container will increase if the molecules are moving faster
If temperature remains constant, but compression is applied, then more molecules are hitting the surface of the container, increasing pressure
Temperature can also increase the rate in which molecules hit the sides faster as well, increasing pressure

18. Changes of State
Many materials change states when heated, either to a liquid, and or a gas
When a solid is heated enough, it breaks the bonds with their neighboring molecules, becoming more disordered in their arrangement, and a liquid
A Liquid heated up with the molecules will move farther apart, becoming a gas,
Liquids boil to become a gas, and boiling is dependent on atmospheric pressures
(less pressure; lower boiling point temp, higher pressure; higher boiling point temp)

19. Gas
A gas will increase in volume by a 1000 as compared to a liquid 99.9% of the volume of a gas is empty space The molecules in a gas are about 10 times farther apart as in a liquid state

20. Evaporation When a liquid changes into a gas without boiling
Becomes a vapor
Faster moving molecules break away from the rest of the liquid
Evaporation causes a cooling affect, as the higher energy molecules break away, reducing the kinetic energy of the molecules, thus dropping the temperature.

21. If air has a density of kg/m3, and a pressure at sea level of pascals, what is the height of the atmosphere?
If seawater has a density of 1030 kg/m3, how many times atmospheric pressure is the pressure at a depth of 30 meters?
Draw three simple diagrams to show how particles are arranged in a solid, liquid, and gas