What are Chemical and Physical Changes?

Evidence of a Physical Change There are three signs that a physical change has occurred (remember, this means that your starting and ending molecules are the same) Change in size Change in shape Change or phase

Evidence of a Chemical Change There are five signs that a chemical change has occurred (remember, this means that your starting and ending molecules are different) Change in Temperature, giving off heat Change in Color, giving off light Change or Creation of Odor Formation of a Precipitate (a solid material) Formation of a Gas

THE DIFFERENCE Physical Change – matter changes form but is still made of the same molecules, typically reversible Chemical Change – a change in the molecules occurs, cannot be reversed

Physical Changes Physical Change – matter changes form but is still made of the same molecules, typically reversible Example: An ice cube melting Solid H2O  Liquid H2O Both the beginning and ending products are made of H2O, the molecules stayed the same

Physical Changes Physical Change – matter changes form but is still made of the same molecules, typically reversible Example: A bag of potatoes is squished up to make mashed potatoes

Physical Changes The digestive system is very muscular and causes physical changes starting with chewing and continuing with churning in the stomach

Chemical Changes The digestive system also causes chemical changes by using enzymes and chemicals to break the food down into its components

The Difference Physical Change – matter changes form but is still made of the same molecules, typically reversible Chemical Change – a change in the molecules occurs, cannot be reversed

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?

How to Separate Mixtures If you have a solution, you can separate out the different parts using chemical or physical methods.

Physical Separation Physical separation techniques use the physical properties of the components to separate them. Physical properties include: State of matter (solid, liquid, gas) Solubility Boiling point Melting point Density Electrical/magnetic properties

Chemical Separation Chemical separation requires that you change one of the molecules in order to remove it from the mixture/solution.