Which is which? How do you know?

Chemical and Physical changes

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.

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… Changes color, form, odor, temperature Can’t be reversed, usually. Chemical Can be reversed easily Same stuff,just in a different form Physical Ummm…stays exactly the same! No change

NOW, YOU KNOW THE DIFFERENCE BETWEEN CHEMICAL AND PHYSICAL CHANGES!