Summary

#### Atomic Theory

“All things are made up of atoms.”

#### States of matter

Solid, liquid, gas, and plasma

#### State of Solids

• Has definite shape and volume
• High density and not very compressible
• Does not depend on the shape of the container (doesn’t fill it in)

#### State of Liquids

• Has a fixed volume
• Takes the shape of container
• Less dense than solids
• Almost incompressible

#### State of Gases

• Takes the shape of the container
• Takes the volume of container (this means that the gas molecules can be spread out evenly in the container or compressed in a smaller container. The volume is when the molecules are evenly distributed.)
• Can be compressed
• Gases are in the gaseous state at room temperature
• Gases have more energy than liquids, and solids.
• Gases are less dense.

#### State of Plasma

Plasma is simply an ionized gas, where the gas is charged with free electrons and positive ions because of the amount of energy plasma contains.

## Unit 1.4 – Heating and Cooling Curves

Heating and cooling curves are a graphical representation of the phase change of a substance. The heating curve of a substance can be determined by heating a solid slowly until it changes to the gas phase while a cooling curve of a substance can be determined by condensing a gas until a solid is formed.

The following curve is a heating curve for ice.
What do you notice?

Why is there a plateau?

• In order for a solid to melt, energy is needed toovercome the intermolecular forces of attraction.
• The heat that warms the ice is used to overcome these forces of attraction, rather than increasing temperature.
• The temperature does not increase until all solid has disappeared.

What would happen if the temperature remained at the plateau?

• There would be a constant change of states from liquid to solid and vice versa.
• This is called dynamic equilibrium because there is an equal change.