Chemical changes vs.
physical changes
 What is matter again?
• Anything that has mass (think weight) and takes
up space.
• Sooooo……. Are the following matter?
 Air
 Water
 Fire
 Earth
 Electricity
 A battery?
 The energy in the battery?
 There
are two types of changes that you
can do to matter.
• Physical changes : a change of matter from one
form to another without a change in chemical
properties.
• Chemical changes: a change that occurs when a
substance changes composition by forming one
or more new substances.
changes do not change a
substances identity.
 Physical
• Ice, water and vapor are all still water! No
matter what state water is in, it still has all the
same properties. It is still made of 2 hydrogen
and an oxygen.
• Dissolving is a physical change
 Like dissolving salt in water, the salt is still there even
though you can not see it, it is there. So how might we
have gotten the salt back?
 Mixtures
(having more than one type of
matter mixed up) can be physically
separated.
• Mixtures are not chemically combined
• Each component of a mixture has the same chemical
make up it had before it was mixed
 Again the salt water, if you had tasted it, it would have
tasted salty and watery (is that the right word?). Even
though you could not see the salt (you could still see the
water though, right!).
 Some mixtures can be hard to separate, but all the
components can be separated. You might have to use
some special techniques. What might
you do?
 Do
not move, there is a chemical change
happening right now!
• What do you breath in? What do you breath out?
This is a chemical change!
• When you let fruit ripen, when you get the
energy from your food, that is a chemical
change.
• When a chemical change happens, new
substances are form, that have different
properties than before.
 What
do you get when you combine the
following and add some heat?
• Flour (grounded wheat, a physical change),
sugar (both white and brown), baking soda,
eggs, butter and if you like some vanilla and or
chocolate.
• If you know, does the new product have the same
properties as any of the reactants?
• Could you figure out a way to get all the
individual components back?
 There
are ways you can tell that a
chemical reaction has occurred.
• Changes in color
• A change in odor (smell is one of the best ways
to tell, be very careful)
• Fizzing or foaming are a good way to see the
changes (remember the pennies).
changes cannot be
reversed by physical changes.
 Chemical
• To get back the original parts of a chemical
change (those you started with), you need to
have another chemical change (and probably
some energy).
• So that means that a cake is a cake, no matter
what physical things you do to it. If you cut it,
freeze it, soak it, cut it again, then again and
again, it’s still a cake, although I would not want
to eat it after all that!
 Chemical
changes can break down
compounds into there elemental parts.
 If you pass electricity through water, you break it
down into the elements that make it up, hydrogen
(explosive) and oxygen (oh sweet breath able live
sustaining element).
 Remember an element is: a substance that cannot be
separated into simpler substances by chemical
means.