1. 1 Physical Changes l Observable characteristics change l Attractions between particles may change – but no bonds break l No change in chemical composition l Often reversible

2. 2 Some examples of physical changes l Changes of state: melting, freezing, boiling, condensing, sublimation… l Changes in size or distribution: grinding, tearing, filtering, decanting, dissolving, crystallizing…

3. 3 Chemical Changes l Bonds break and atoms rearrange l Not easily reversed l “Endothermic”: takes in heat (makes the surroundings colder) l “Exothermic”: releases heat (makes the surroundings warmer) l Reactants Products

4. 4 Some words that indicate chemical reactions l burn l rot l rust l decompose l ferment l explode l Oxidize l Can you think of others?

5. 5 Some clues for chemical reactions l Gas or vapor forms: C 12 H 22 O 11 C + H 2 O l Precipitate forms: (solid forms in liquid mix): AgNO 3 + NaCl AgCl + NaNO 3 l color change: Cu + HNO 3  Cu(NO 3 ) 2 + NO 2 + H 2 O l light emitted – fireworks l odor forms l energy produced or absorbed:

6. 6 …more l light emitted – fireworks l odor forms – rotting food l energy transferred - hand warmers Fe + O 2 Fe 2 O 3 + heat

7. 7 Conservation of Mass and Energy l Neither mass nor energy are created or destroyed during a physical or a chemical reaction l Even if there is a change of state or a rearrangement of atoms, the matter still exists, and the energy was transferred.