2.5 Physical and Chemical Changes

Chemical Change A chemical change is any change where you change a substance chemically. A new substance is created Example: Lighting a match

Evidence of a Chemical Change Chemical Changes occur when: …there is a change in color … there is a production of gas … there is a formation of a precipitate

Physical Changes Physical Change- a change that takes place that does NOT change the substance chemically. Examples: haircut, ice melting

Physical Changes States of Matter Solids: Have a definite shape and a definite volume Slow molecules, low energy Liquids: Definite volume but not a definite shape Medium energy molecules Gases: No definite shape, no definite volume Fast molecules, high energy

Phase Changes A phase change is a reversible physical change that occurs when a substance changes from one state of matter to another. Energy is either absorbed or released during a phase change. Endothermic – energy is absorbed Exothermic – energy is released

Physical Changes Melting: Solid to liquid, endothermic

Physical Changes Freezing: Liquid to solid, exothermic

Physical Changes Evaporation: Liquid to gas, endothermic

Physical Changes Condensation: Gas to liquid, exothermic

Physical Changes Sublimation: Solid to gas, endothermic

Physical Changes Deposition: Gas to solid, exothermic