Physical Change
DEF: The physical properties of a
substance change, but the identity of
the substance does not change.
Examples of Physical Changes

States of matter (solid, liquid, gas):
ice
H2O
steam
Although water is in the form of ice it still
has the same chemical composition (H2O)
Examples of Physical Changes
Tearing a piece of paper
 Chopping wood
 Glass Breaking

Examples of Physical Changes
Mixtures:
 Adding red food coloring to water
 Sugar and salt dissolve in water

Chemical Change
DEF: A chemical change is when matter
has changed into a new substance through
a chemical reaction.
What is a chemical change?

The animation to the right shows a
chemical change. The blue and
white molecule is more attracted
to the red and white atoms than
the green atom so they switch,
forming a new substance.
Animation from: http://www.ias.ac.in/initiat/sci_ed/resources/chemistry/sn2.gif
Why did baking soda and vinegar
bubble?

A chemical change occurrs when you combine
baking soda and vinegar.
◦ Vinegar makes the water more acidic.
◦ When the molecules in baking soda mix with the acid,
some of their atoms are more attracted to the acid and
they break apart to form new molecules.
Baking
Soda
Baking soda and vinegar are like two
couples dancing. When they are
separate from each other they stay
with their own molecule…
Vinegar
Why did baking soda and vinegar
bubble?

A chemical change occurred when you combined
baking soda and vinegar.
◦ Vinegar makes the water more acidic.
◦ When the molecules in baking soda mix with the acid,
some of their atoms are more attracted to the acid and
they break apart to form new molecules.
Baking
Soda
Vinegar
But when the two molecules mix,
atoms from one molecule are
more attracted to the other
molecule…
Why did baking soda and vinegar
bubble?

A chemical change occurrs when you combine
baking soda and vinegar.
◦ Vinegar makes the water more acidic.
◦ When the molecules in baking soda mix with the acid,
some of their atoms are more attracted to the acid and
they break apart to form new molecules.
Sodium, and
other stuff
CO2
H2O
…So they switch dance partners
and form new substances.
Notice that nothing was created or
destroyed… just changed.
Evidence for a Chemical Change
1. Formation of a gas
Evidence for a Chemical Change
2. Color Change
◦ Seeing a color change after mixing substances together is
evidence that a chemical change took place.
From: http://www.youtube.com/watch?v=yqUghaS5apk
Why did red cabbage juice turn
the powders different colors?

A chemical change occurred when red cabbage juice
was added to cream of tartar and laundry detergent.
◦ Red cabbage juice is an indicator, because it contains
molecules that change color when an acid or base is added
to them.
◦ Cream of tartar is an acid, so it gave particles to the
indicator, making it turn from blue to pink.
◦ Laundry detergent is a base, so it took particles from the
indicator, making it turn from pink back to blue.
Evidence for a Chemical Change
3. Temperature Change
Evidence for a Chemical Change
Formation of a Precipitate
4.

When mixing two substances together a new
solid forms. This is called a precipitate.
Iron + Oxygen = Rust
Is it a Chemical Change?

Write down “YES” on your
paper if it is a chemical
change, and “NO” if it isn’t.

If YES, list what evidence
supports this. (Example: gas
formation).
Is it a Chemical Change?
A forest fire destroys acres
of land. There is a lot of
smoke, and the trees
turn to charcoal.
ANSWER:
EVIDENCE:
YES
- Smoke, - color change,
- temperature change
Is it a Chemical Change?
When making hot cocoa,
clear water turns brown
when you mix the cocoa
in.
ANSWER:
No
(the water is turning brown
because the cocoa is brown)
Is it a Chemical Change?
An old wheelbarrow is left
out in the rain and
rusts.
ANSWER:
Yes
EVIDENCE: Color change, precipitate
forming (rust)
Is it a Chemical Change?
On a hot day, water forms
on the outside of a cold
glass of water.
ANSWER:
No
(No new substance is forming)
Is it a Chemical Change?
Ice cream melts after it
falls on the ground.
ANSWER:
No
(No new substance is forming)
Is it a Chemical Change?
A raw egg gets cooked.
ANSWER:
Yes
EVIDENCE: Color change
Is it a Chemical Change?
When Alka Seltzer is
dropped into water
it fizzes.
ANSWER:
Yes
EVIDENCE: gas formation
Is it a Chemical Change?
Crayons change white
paper to red.
ANSWER:
No
(The paper is turning red because the crayon
is red.)
Is it a Chemical Change?
Soda fizzes, and bubbles
rise as you pour it in a
glass.
ANSWER:
No
(The bubbles were already there, just under
pressure in the bottle.)
Is it a Chemical Change?
When you crack a glow stick,
hydrogen peroxide mix
with other chemicals,
causing it to glow and
warm up.
ANSWER:
EVIDENCE:
Yes
- color change
- temperature change