Chemical and Physical Changes

Chemical vs. Physical Changes Physical Change – involves a change in appearance but does not involve creation of new materials. Chemical Change – involves the formation of new materials.

Examples of Physical Changes Changes in state – i.e., a solid melting into a liquid and then evaporating into a gas Melting and solidifying of wax Sharpening a pencil Tearing up paper Rock breaking into several pieces

Examples of Chemical Changes Rusting Digesting food Burning materials Fruit ripening Mineral formation in igneous rock

Chemical Changes The process that brings about a chemical change is called a chemical reaction The new materials that get created are called products and the starting materials are called reactants Chemical changes are usually not easy to reverse

Chemical Changes Chemical reactions are characterized by a number of changes including: Color changes Formation of a precipitate (cloudy solution) Formation of gas (bubbles) Release of light Release of heat

Chemical Changes There are many words associated with chemical changes. Some examples include: Burned, burning, burns Changed, changing, changes Combined, combining, combines Formed, forming, forms, formation

Chemical Changes For each of the following sentences, find the word that indicates a chemical change occurred.

Sentence #1 Gasoline in cars is burned, releasing gases into our atmosphere

Sentence #2 Rust forms on an iron pipe after being exposed to moist air for many years.

Sentence #3 Nitrogen oxide emissions combine with water vapor, producing nitric acid

Reflect and Review What is the difference between chemical and physical changes? Name two examples of chemical changes. Name two examples of physical changes. What are 5 characteristics of a chemical change? List three words that are commonly associated with chemical changes.