All materials on Earth have unique physical properties that help scientists identify them. Matter can undergo two main types of changes: physical changes (where the material itself stays the same) and chemical changes (where a completely new substance is formed).

1. Physical Changes: Same Substance, Different Form

A physical change alters the shape, size, or state of matter without changing what the material is made of. The internal makeup of the substance remains identical.

• Examples: Cutting, folding, tearing, crushing, and dissolving (e.g., mixing Kool-Aid powder into water).

• States of Matter: Changing from a solid, liquid, or gas is always a physical change caused by adding or removing heat energy.

The Three States of Matter & Particle Behavior

State Shape & Volume Particle Movement Water Example

Solid Keeps its own shape and volume Packed closely in a rigid structure; vibrate in place Ice

Liquid Takes the shape of its container Closely packed, but slide freely past one another Liquid water

Gas Expands to fill the shape and volume of container Spread far apart; move freely at a rapid pace Water vapor / Steam

2. Key Phase Transitions for Water

Adding or removing thermal energy (heat) changes the state of water. These transitions occur at precise temperatures:

                      + Heat (Melts)                 + Heat (Boils)

  [ Solid: Ice ] ──────────> [ Liquid Water ] ──────────> [ Gas: Water Vapor ]

                 <──────────                  <──────────

                - Heat (Freezes)                       - Heat (Condenses)

• Freezing & Melting Point (0 degrees Celsius/ 32 degrees Fahrenheit): Water freezes into ice when cooled below 0 degrees Celsius. Ice melts into liquid water when heated above 0 degrees Celsius.

• Boiling & Condensation Point (100 degrees Celsius/ 212 degrees Fahrenheit): Liquid water boils into gas (water vapor) when heated to 100 degrees Celsius. Water vapor cools down and condenses back into liquid water at the same temperature (e.g., water droplets on a cold soda can).

3. Chemical Changes: Forming New Substances

A chemical change (or chemical reaction) occurs when materials react to form brand-new substances with entirely different properties.

Clues a Chemical Change Has Occurred:

• Gas or Odor Production: Bubbles or new smells appear (e.g., mixing vinegar and baking soda).

• Color Change: Unplanned color shifts occur (e.g., rust forming on iron exposed to water).

• Temperature Change: Energy is released or absorbed, making it feel hot or cold.

• Precipitate Formation: A solid forms from mixing two liquids.