1. Chapter 20 – Chemical Reactions 20.1 – Chemical Changes Physical change occurs when only the physical properties of a substance changes. Evidence: change in state of matter, size, or shape http://www.learner.org/courses/essential/physicalsci/session4/closer1.html

2. Chemical change occurs when a change happens that results in a new substance forming. Evidence: color change, bubbling, turning cloudy, or temperature change

3. 20.2 – Chemical Equations Chemical reaction involves rearranging the atoms in the reactants to form the products. All chemical reactions either use or produce energy. If it loses (produces) energy, the reaction is exothermic If the reaction gains (uses) energy, it’s endothermic

4. The chemical equation is a recipe for a chemical reaction. A chemical equation uses chemical formulas and symbols to represent a reaction instead of words.

5. MUST DRAW Subscript

6. Diatomic molecules: Bromine, Oxygen, Nitrogen, Chlorine, Hydrogen, Fluorine CPO IPC Textbook

7. Since only whole atoms can exist it is necessary to balance equations. To balance, there must be an equal number of each element on each side.

8. MUST DRAW

9. 20.3 – Conservation of Mass French scientist, Antoine Lavoisier, established that the total mass of the products are equal to the total mass of the reactants. This is the law of conservation of mass.