Chemical and Physical Changes

DEMOS Write down your observations during the DEMOS your teacher does on your Lab Sheet under EVIDENCE of a change. Determine if you believe the DEMO shows a CHEMICAL or PHYSICAL change or BOTH.

DEMO What happens when you mix sulfuric acid and table sugar?

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

How can you tell which change it is? Chemical Change - Substance changes into something new. You can tell because of color change, heat or light given off or taken in, precipitate, gas bubbles; new substances form. Physical Change - Substance doesn’t change to something new, it may change form, shape, size or phase but it is still the same stuff. It is reversible and sometimes requires heat from the outside to make it happen but does not release heat by itself.

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

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

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 in Phase of Matter

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 Change in Color Change or Creation of Odor Formation of a Precipitate (a solid material) Formation of a Gas

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?

Chemical or Physical Change?