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

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

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

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.

MUST DRAW Subscript

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

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.

MUST DRAW

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.