chemical and physical changes
Post on 23-Feb-2016
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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!
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