Understanding Chemical and Physical Reactions
A lesson on physical and chemical reactions.
• To introduce students to the two types of reactions.
To teach the signs of a physical change.
To teach the signs of a chemical change.
To explain the differences between a physical and chemical reaction.
To present exercises that test students? understanding of chemical and physical reactions and how they differ.
To present exercises that test student?s ability to identify physical and chemical changes.
The first way matter can change is through a physical reaction. A physical reaction causes the matter to shift shape or state. For example, if you crush a cardboard box, only the shape changes. It has the same molecules, and is still a cardboard box, even if it is flat. This is a physical reaction. Another kind of physical reaction is an ice cube melting. As it melts, the ice changes from a solid to a liquid state. Even though it is no longer frozen, the matter is still water. That makes it a physical change.