Chapter 2.3Changes of Matter

Review What is the difference between a

homogeneous and heterogeneous mixture? Provide one example of each.

Compare and Contrast molecules and compounds.

Physical Changes Physical Change – a change of matter

from one form to another without a change in chemical properties

Examples

Physical Changes Physical changes do not change a

substance’s identity.

Example An ice cube melts into water The water is then heated to form a gas

In both cases, it is still water.

Dissolving is a physical change When you pour salt into water, the salt

dissolves.

The salt molecules become spread out between the water molecules.

The molecules of salt and water do not change.

Chemical Changes Chemical Change – happens when one

or more substances are changed into entirely new substances that have different properties.

Examples

Chemical Changes Chemical changes form new substances

Cannot be reversed by physical means

Anytime food is cooked, it is a chemical change

Signs of a chemical change Production of gas

Change in odor

Production of sound, heat, or light

Breaking down mixtures and compounds Mixtures can be separated by physical

changes, but compounds must be broken down by chemical changes