ChangesPhysicalReversibleIrreversibleChemical The world around us (matter) is always in a a state of flux. All changes involve some form of energy transfer. EXAMPLES?

Phase Changes are Physical Changes Whether solid in the form of ice, as a liquid or as a gaseous vapor, water is always H 2 O. Water always has a ratio of two hydrogen atoms to one oxygen atom regardless of the form it is in. O HH Phet App: States of Matter

3 SOLID LIQUI D GAS MELTING FREEZING EVAPORATION CONDENSATION SUBLIMATION DEPOSITION Physical Changes

The internal composition of something does not change. It remains the same chemically. Examples: Ripping paper, crushing a can, cutting hair, breaking chalk, molding Play-Doh cracking an egg. 4 Aluminum Aluminum foil is made up of aluminum atoms. Tearing aluminum foil in half still results in aluminum atoms

Two Types of Physical Changes Irreversible Physical Change: something that cannot be undone. For example, you cannot uncrack an egg or uncut hair. Reversible physical change: a change that can be reversed. Phase changes are reversible. Ice that melts can be refrozen. 5

Burn Burn Burn

Chemical Changes One or more substances changes into something new. The internal properties of a substance change. Example: Burning Paper (combustion in general), digestion of food, rusting, fireworks exploding, cooking an egg, any chemical reaction. 7 Something New forms at the Molecular Level

FeFe FeFe FeFe FeFe FeFe FeFe FeFe FeFe Combustion of Steel Wool 4Fe+ 3O 2 ---> 2Fe 2 O 3 O O O O O O O O O O O O +  FeFe FeFe FeFe FeFe O O O O O O FeFe FeFe FeFe FeFe O O O O O O 4 iron atoms (4Fe) combine with 6 oxygen (3O 2 ) atoms to form two units of iron oxide (2Fe 2 O 3 )

Electrolysis of Water 2H 2 O + electricity  2H 2 + O 2  2 water molecules (2H 2 O) split into 4 hydrogen atoms (2H 2 ) and 2 oxygen atoms (O 2 ), O HH O HH H H H H + O O

5 Clues a Chemical Change might have taken Place Transfer of Energy (temperature change…endothermic/exothermic reactions) Color Change (ex. Fruit changes color over time, this is a chemical change) Formation of a Precipitate (a solid particle when two solutions are mixed) Production of Gas (gas bubble indicate a chemical change might have occurred) Production of an Odor (an egg rotting, smell of the atmosphere after a lightning storm) Lab