Which is which? How do you know? Chemical and Physical changes • Matter can change form! • Two major changes are CHEMICAL and PHYSICAL. • Let’s see what the differences are…. PHYSICAL CHANGES • It is the SAME substance – just changes form. PHYSICAL CHANGES • It is the SAME substance – just changes form. One example of a Physical Change • Water can freeze! But it is still water, no matter what form it is in. More examples of Physical changes • A piece of clay can be formed into something else. • Someone’s hair can be cut or colored. • A pencil can be broken. • The form is changed but the matter stays the same. Clay is clay. Hair is hair and a pencil is still a pencil. CHEMICAL CHANGES • In a chemical change, the substance changes into something else entirely! • Sometimes is resembles the original matter; other times it looks totally different. • It usually cannot be reversed. Signs of a CHEMICAL change • A chemical change has hints and tell-tale signs: • • • • • Color change Releases energy Can give off an odor Produces gases or solids It is not easily reversed CHEMICAL CHANGES • In a chemical change, the substance changes into something entirely different. It is not easily reversed. Chemical change Stinky!!!!!! Peeeuuuu! • Yes, as a fish decomposes, the sure does give off an odor! Chemical change..Energy release! Will it be a Chemical or Physical Change? Energy release! What was it? Chemical or physical or both? • Right! There was a chemical change. Light and heat were given off, there was an odor, you cannot reverse the fire cracker….but did the paper and materials of the firecracker change, too? • Mostly, this was a chemical change but probably a few physical changes, too. Color change – Chemical change Chemical change • Coal is a rock made up from ancient plants. • It can burn! Not easily reversed – chemical change! CHEMICAL OR PHYSICAL CHANGES? WHICH IS WHICH? • LET’S TRY A FEW EXAMPLES! • READY? Chemical or Physical Change or No change? • Water goes through a dam and turns a turbine. Electricity is a result. But, be careful, does the water itself change into electricity? Chemical, physical or no change. • The liquid water stays liquid water. • The water does work, however, and helps the turbines in the dam make electricity. Chemical, Physical or No change? This is a gas stove burner. Which was it? • CHEMICAL change, right? • The gas is burning and changing to a flame. • The flame gives off heat and some light. • You cannot change the flame back into the natural gas. • Some natural gas has a bad odor. Let’s review! • Physical Changes: • The substance just changes form. • Solid to liquid; liquid to solid; liquid to gas. • It stays what it was originally and most times CAN be reversed. Chemical Changes • • • • • These result in: - odors - heat and or light given off (energy) Cannot be easily reversed Color change • Or any combination of these. • 1. What change do you see when you make a paper snowflake? • 2. What change do you see when you light a match? • 3. What change do you see when you make Oobleck? (Be careful!) Physical change! When you cut paper into a snowflake, you are only changing the physical part – it is still the same paper. You light a match and it flames up. • It gives off heat and light, it changes color, it has an odor, and you cannot easily change the burnt match back into a normal, unburned match – right? • Soooo, it is a chemical change. Now, the hardest one! • Oobleck is a substance made up of only corn starch and water. Sometimes it acts like a solid. Other times like a liquid. When you make it, is this a chemical or physical change or no change? • • • • • Does Oobleck change color? Does Oobleck give off light, or any energy? Does Oobleck give off an odor? Does Oobleck produce a gas? Could you reverse it – for example, take away the water and leave dry cornstarch? RIGHT! • It is a physical change. The water can be evaporated away and the dry cornstarch left. There is no energy release, no odor created, no light, nothing. Let’s Review… Chemical Physical No change • Changes color, form, odor, temperature • Can’t be reversed, usually. • Can be reversed easily • Same stuff,just in a different form • Ummm…stays exactly the same! • NOW, YOU KNOW THE DIFFERENCE BETWEEN CHEMICAL AND PHYSICAL CHANGES!