CHEMICAL AND PHYSICAL CHANGES

CHEMICAL AND PHYSICAL CHANGES

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….

• READY????

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!

WOW….it is the 4th of July and you have a huge firecracker to

set off!

Will it be a Chemical or Physical Change?

Energy release!

What was it? Chemical or physicalor 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.

• No change here!

• 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.

QUICK QUIZ

• 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.

THINK!!!

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 formPhysical

• Ummm…stays exactly the same!No change

Congratulations!

•NOW, YOU KNOW THE DIFFERENCE BETWEEN

CHEMICAL AND PHYSICAL CHANGES!