Physical vs. Chemical Changes

Goal: How do you tell the difference between chemical and physical changes?

Physical Change* A change in any object’s physical properties any change in an object’s: - mass- color - weight- shape - volume- hardness - density- texture

Physical Changes* Changes in Density, Mass or Volume D = M/V

Physical Changes* Creating mixtures that can be separated out - mixtures can be reversed.

Physical Changes* Changes in Phase of Matter

Example of a Physical Change: A Melting Icicle

physical properties = characteristics of a substance that can be observed without changing the identity of the substance. ex.) wood is still wood whether it is shaped into a baseball bat or used to build the walls of your house – or if it’s still in the shape of a tree! ex.) water is still water whether it is in the form of ice, liquid water, or water vapor. It’s still H 2 O!

Review: Other Physical Properties* Color Size Shape Texture Magnetism

Chemical Changes* Chemical Changes occur when atoms react with other atoms to form chemical bonds. When atoms are bonded together they make a molecule.

Chemical Changes* When a chemical reaction happens the new molecules are a new substance or compound. A + B  AB

Chemical Change > changes that substances undergo when they turn into other substances > Also called a “Chemical Reaction” ex.) as coal burns, O 2 (in the air) combines chemically with C (the substance that makes up most of the coal) and forms a completely new substance = CO 2 - C and O 2 have changed chemically! They no longer exist in their original forms! - Written out: C + O 2 = CO 2

Evidence of Chemical Changes, Reactions or Bonding Energy being taken in or given off (heat, coolness, light)

Evidence of Chemical Changes, Reactions or Bonding Gas or Bubbles

Evidence of Chemical Changes, Reactions or Bonding Color or Texture Change

Evidence of Chemical Changes, Reactions or Bonding Color and Texture Change that is not easily reversed

Evidence of Chemical Changes, Reactions or Bonding Forming of a Precipitate (adding to solutions and a solid is formed)

How to decide type of change Ask yourself: Can I easily turn substance back to the way it was? If yes: physical change If no: chemical change Was the change awesome to watch? If yes: Probably chemical change If no: Probably physical change Did the name of the new substance change? If yes: Probably chemical If no: Probably physical

Examples of Chemical Change* –The rusting of iron –The baking of bread –Burning of a match –Fireworks

Example of a Chemical Change: The Electrolysis of Water (H 2 O) The Chemical Identity of Water ( H 2 O ) is changed into the elements Hydrogen ( H 2 ) and Oxygen ( O 2 )