Physical Versus Chemical Changes Objective To differentiate between

Physical Versus Chemical Changes Objective • To differentiate between physical and chemical changes in matter

Physical Changes �During a physical change, the composition of matter never changes �The substances present before the change, are the same substances present after the change �Only changes what the substance looks like, not it’s identity �Example: Ripping paper

Chemical Changes �During a chemical change, the composition of matter always changes �Something new is made �It is also called a chemical reaction �Example: Burning paper produces CO 2, H 2 O and ash

Changes in Energy �Energy is always absorbed or given off in a chemical reaction �This also may happen during a physical change as well �Many times this is in the form of heat (may be in the form of heat, light etc. )

A change of energy in the form of heat can happen in two ways Exothermic Process �A process that releases heat to the surroundings �These reactions make the surroundings get warmer �Example: fire �Exothermic Reaction Endothermic Process �A process that absorbs heat from the surroundings �These reactions make the surroundings get cooler �Example: chemical ice packs �Endothermic Reaction

Changes in Matter Physical Changes �A change of a substance that does not affect its chemical composition �The substance does not become a different substance �The identity of the substance stays the same �May be a phase (state) change �May involve a change in energy Chemical Changes (Reactions) �The changing of substances into other substances �Always involves a change in energy �Physical changes often occur along with chemical changes

To decide if a change is chemical or only physical ask: �Did the substance become something new? (Did it change its identity? ) �If yes = chemical change �If no = physical change �Can the substance be changed back easily? �If yes = physical change �If no = chemical change