chemical and physical changes

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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:
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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
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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?
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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!

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