Physical and Chemical Changes

What is the difference between physical and chemical properties?

Physical Change Although some extensive properties (like shape, phase, etc.) of the material change, the material itself is the same before and after the change. The change can be “undone.”

Chemical Change The substances present at the beginning of the change are not present at the end; new substances are formed. The change cannot be “undone.” (Exception: Some reactions are reversible.)

Physical or Chemical Change? How can you tell?

Physical or Chemical Change? How can you tell? Rusty Nail

Physical Changes Aluminum foil is cut in half. Clay is molded into a new shape. Butter melts on warm toast. Water evaporates from the surface of the ocean. A juice box in the freezer freezes. Rubbing alcohol evaporates on your hand.

Chemical Changes Milk goes sour. Jewelry tarnishes. Bread becomes toast. Rust forms on a nail left outside. Gasoline is ignited. Hydrogen peroxide bubbles in a cut. Food scraps are turned into compost in a compost pile. A match is lit. You take an antacid to settle your stomach. Your body digests food. You fry an egg.

Physical or Chemical Changes? Salt or sugar dissolving in water The formation of steel or brass (metal alloys) Inhaling oxygen and exhaling carbon dioxide Source: A Closer Look: Chemical Vs. Physical Change http://www.learner.org/channel/courses/essential/physicalsci/session4/closer1.html