The document outlines 6 key indicators of chemical change: 1) A change in color 2) Production of gas or bubbles 3) Formation of a precipitate or solid 4) Absorption or release of energy 5) A change in odor 6) Chemical changes are not easily reversible unlike physical changes which do not alter the composition of the original substance.

1. INDICATORS OF CHEMICAL
CHANGE
• Here are 6 indicators of chemical
change
Source: http://www.ric.edu/faculty/ptiskus/chemical/

2. 1) CHANGE IN COLOUR
• As in the case of autumn leaves, a change in color is
a clue to indicate a chemical change.
• Perhaps you have found a half eaten apple that
turns brown.
• The reason is that a chemical change has occurs
when food spoils.
Source: http://www.ric.edu/faculty/ptiskus/chemical/

3. 2) PRODUCTION OF GAS (BUBBLES)
• The formation of a gas is a clue to chemical
changes.
• The bubbles of gas that you
observed form when an antacid
is dropped into water is an
example of change.
Source: http://www.ric.edu/faculty/ptiskus/chemical/

4. 3) PRECIPITATE FORMS
• Another clue that a chemical change has occurred is the
formation of a solid.
• A solid that separates out of solution during a chemical
change is called a precipitate. (click on link for example)
• PRECIPITATE IS THE FORMATION OF A SOLID DUE TO CHEMICAL CHANGE
Source: http://www.ric.edu/faculty/ptiskus/chemical/

5. 4) ENERGY (ABSORBED OR RELEEASED)
• Another sign of a chemical change is the release or gain of
energy by an object.
• Many substances absorb energy to undergo a chemical change.
• Energy is absorbed during chemical changes involved in
cooking, like baking a cake.
• When you bake a cake, energy is absorbed by the batter as it
changes form a runny mix into a cake.
Source: http://www.ric.edu/faculty/ptiskus/chemical/

6. 5) ODOUR CHANGES
• It only takes one experience with a rotten egg to learn that
they smell different that fresh eggs.
• When eggs and food spoil, they undergo a
chemical change.
• The change in odour is a clue to the chemical change
• When you smell an odd order in foods such as chicken,
pork of mayonnaise, you know that the food has
undergone a chemical change. You can use this clue to
avoid eating spoiled food and becoming ill.
Source: http://www.ric.edu/faculty/ptiskus/chemical/

7. 6) CHEMICAL CHANGES ARE NOT EASILY
REVERSED
• In a chemical change the composition of a
substance changes
• After it has changed it is very hard to change it back
• For example: As wood burns, it turns into a pile of
ashes and gases that rise into air. After the wood is
burned, it cannot be restored to its original form as
a log.
Source: http://www.ric.edu/faculty/ptiskus/chemical/

8. DIFFERENCE BETWEEN A PHYSICAL
CHANGE AND CHEMICAL CHANGE
• How do physical and chemical changes differ from each other?
• Think about ice for a moment.
• After ice melts into liquid water, you can refreeze it into solid ice
if the temperature drops.
• Freezing and melting are physical changes.
• The substances produced during chemical changes however
cannot easily change back into the original substances
• For example burning wood into ashes cannot be turned back to
wood

9. DIFFERENCE BETWEEN A PHYSICAL
CHANGE AND CHEMICAL CHANGE
• The most important thing for you to remember is
that in a physical change the composition of a
substance does not change and in a chemical
change the composition of a substance does change