Chemical & Physical Changes Today we're going to be going over what makes the difference between a chemical and a physical change. As we go through these, try to think back to your labs and recall which changes you observed.

Physical Changes Physical changes are changes that do not affect the chemical nature of the substance being changed...This means that one or more of the physical properties of the material has been changed... What are some physical properties????

Physical Properties ·Texture ·Size ·Shape ·Color ·Volume ·Mass ·Weight ·Density

Examples...

Chemical Changes Chemical changes happen when bonds are broken between atoms and new bonds are formed. There are many different types, which we will discuss a little later in the semester. The biggest thing to remember about chemical changes is that in a chemical change, the composition of matter always changes. Chemical changes will often also be called chemical reactions.

Chemical reactions cause changes in energy ·Endothermic - A reaction that absorbs energy in the form of heat ·Exothermic - a reaction that emits energy in the form of heat

Chemical Properties Like physical changes, chemical changes are only known to occur when a chemical property of a substance changes. What then are some chemical properties that you can see change? (These are more difficult than physical properties because it involves a complete change in substance)

Chemical Properties ·Odor ·Color (can also be physical, this one is really tricky) ·Change in Energy ·Change in Form ·Light, heat, or sound given off ·Formation of Precipitate ·Formation of gases ·Decomposition

Examples...

Important Fact on Mass Law of Conservation of Mass - No matter what chemical reaction you have, the mass of your products will always equal the mass of your reactants