Physical and Chemical ChangesNew stuff is buff…

• A physical change is a change that affects one or more physical properties of a substance.

• The appearance, shape, or size of a substance may be altered during a physical change.

• Physical changes, such as changes in state (boiling water), dissolving sugar in water, cutting paper, or crushing an aluminum can do not change the chemical identity of a substance.

Physical changes:

Physical Changes of Matter

Ice Melting Water boiling Crushing a can

Physical Changes: Identification and Reversal

Some, but not all physical changes can be reversed.

You could refreeze the water into ice, or bend a wire back into a straight shape, but you cannot put your hair back together if you don’t like your haircut!

• A chemical change is the process by which one or more substances change into entirely new substances.

• Chemical changes are not the same as chemical properties.

• When the particles and chemical bonds that make up a substance are rearranged, a chemical change has taken place. It usually cannot be reversed without another chemical change.

• Another name for a chemical change is a chemical reaction.

Chemical Changes

5 Signs of a chemical change: • 1. Color change• 2. Precipitation• 3. Gas production• 4. Temperature

change• 5. Characteristic

property change

Observing two or more of these signs during a change means you are likely observing a chemical change.

Chemical Change signs: Color change• The change of color should be due

to some internal reaction of the material or substance NOT due to the addition of a colorant or dye.

• Examples: leaves changing color are a chemical change, but adding color dye to a material (on the outside of the material) is NOT a chemical change as long as it can be reversed. However, tie-dyeing a shirt IS a chemical change because it changes the fibers of the cotton in the shirt.

Chemical Change signs: Precipitation

• Precipitation – the solid that forms from a solution during a chemical reaction.

• It looks like a cloudy solid in an otherwise clear solution.

Chemical Change signs: Gas Production• Odors can be produced during a

chemical change.

• Fizzing and foaming may mean gases are being produced.

• The production of gas is often evidence of a chemical change.

• Boiling also can produce gas bubbles, but boiling is a physical change.

Chemical Change signs: Temperature• As particles of chemicals interact,

they can take in or give off thermal energy, thus changing the temperature. A chemical change that gives off heat is called exothermic, while one that takes in heat (gets cooler) is called endothermic.

Chemical Change signs: Characteristic Properties

• Energy changes from one form to another can be evidence of a chemical change.

• Light given off from a reaction (chemiluminescence) is often a sign of a chemical change.

Type of Change Physical Chemical

Melting ice

Burning wood

Souring milk

Wadding up paper

Rusting metal

Corn Starch and Water

Corn Plastic

Chart of some Physical and Chemical Changes:

Chemical or Physical Change?

• Cutting paper?• Physical

Chemical or Physical Change?

• Toast burning?• Chemical

Chemical or Physical Change?

• Disappearing puddle?

• Physical

Chemical or Physical Change?

• Rocket fuel burning?• Chemical

Chemical or Physical Change?

• Metal rusting?• Chemical

Chemical or Physical Change?

• Candle burning?

• Chemical

Physical or Chemical Changes: mneumonic idea…