Download Lesson 2 – Physical and Chemical Changes Lesson

Physical and Chemical Changes
SNC2D
Physical Change
 A change (of state or form) in which a new substance is not
formed and you can get the original substance easily.

Change involving:
Melting, boiling, evaporation/condensation,
crystallization, dissolving
Chemical Change
 A change in which a new substance is formed and you cannot get the original
substances back easily.

How to recognize a chemical change:
1. A new substance is produced
2. A new odour/taste and/or colour is produced
3. heat or light is produced
4. Bubles of gas are formed
5. A precipitate (insoluble solid) is formed
Using the information above, complete the following table:
Change
A pie is baked
P
Chocolate melts


A match is lit
Wood is rubbed with
sandpaper
An iron bar is heated until
its red hot
A banana turns brown




A day old fish begins to
smell
A balloon bursts

Your hair is cut

Ashes form when wood is
burned
C


Why?
Change
Broken glass is crushed
P
C

Wire rusts

A firecracker goes BANG

A silver spoon tarnishes

Sugar is dissolved in coffee
Why?

Milk turns sour

Place a check in the appropriate column:
Change
Salt dissolves in water.
Physical
Change
yes
Hydrochloric acid reacts with magnesium to produce hydrogen gas.
yes
A piece of copper is cut in half
yes
A sugar cube is ground up.
yes
Water is heated and changed to steam.
yes
Iron rusts.
yes
Ethyl alcohol evaporates.
yes
Ice melts.
yes
Milk sours (goes bad).
Sugar dissolves in water.
Chemical
Change
yes
yes
Sodium and potassium react violently with water.
yes
Pancakes cook on a griddle.
yes
Grass grows on a lawn.
yes
A tire is inflated with air.
yes
Food is digested in the stomach.
yes
Water is absorbed by a paper towel.
yes
Ethyl alcohol boils at 79°C.
yes
Paper burns.
Water freezes at 0°C.
yes
yes
Change
Fireworks explode.
yes
Alka-Seltzer gives off carbon dioxide when added to water.
yes
Clouds form in the sky.
yes
Now your knowledge of the two types of changes will be put to the test! Classify the changes
listed below as either physical or chemical, and then give a reason for your decision. The first
one has been done for you!
Change
A newspaper yellowed
after a few weeks
The steel wool turned the
black pot a shiny silvery
colour
Acid caused limestone to
fizz
The back steps are rotting
out
Spilled gasoline dried but
left a bad odour in the
room
The gravy in the
refrigerator jelled
Red meat turned brown as
it cooked
You got a cavity in your
tooth
The paint on your car
turned dull
Type
Reason
Chemical
Colour change is permanent
Physical
Steel wool removed burnt food from pot. No
new substances formed in the process
Chemical
Chemical
The fizzing is carbon dioxide gas that forms
when the acid reacts with the calcium
carbonate that makes up the limestone
Microorganisms, insects and worms are
digesting the wood breaking cellulose into
simpler compounds. There is a change in
colour and odour.
Physical
State changes like evaporation are physical
changes
Chemical
The strands of protein reacted with one
another forming cross-linking that holds
them together to make a solid. If you heat
the gravy, the bonds break and the gravy
become a liquid
See:
http://www.sciam.com/article.cfm?id=whatis-jell-o-how-does-i
Chemical
Change in colour, odour and taste.
Chemical
Physical
The rotted part of the tooth is a new
substance. Acid produced by bacteria
digesting sugar results in a chemical reaction
between acid and tooth enamel
No new substance is formed. The paint
wears out over time.