1. Chemical Change
Observing, Describing,
Controlling

2. Observing Chemical Change
• Matter can be described in two
ways:
– Chemical properties
– Physical properties

3. Observing Chemical Change
• Chemical Properties: The
characteristics of a substance that
describes it’s ability to change into a
different substance.
– EXAMPLE: In our magnesium lab, we lit
the magnesium on fire, watched it burn
as it reacted with the oxygen in the air.
This was its chemical property:
flammability.

4. Observing Chemical Change
• Physical Properties: a characteristic
of a substance that can be
observed without changing the
substance into something new.
– EXAMPLE: Frozen water (ice) melts at 0
degrees Celsius. The tops of the tables
in this room are black and 4.5ft long.

5. Observing Chemical Change
• Like the properties of matter, the
changes it undergoes can be:
– Physical Changes
OR
– Chemical Changes

6. Observing Chemical Change
• Physical Changes: Any change that
alters the form, shape, or
appearance of a substance but
does not change it into a new
substance.
– EXAMPLE: If I were to toss fresh berries
into a blender and make a fruit
smoothie- it would still be fruit, just
mashed into smaller pieces.

7. Observing Chemical Change
• Chemical Changes: a change that
a substance undergoes where a
totally new substance is the result.
– EXAMPLE: In the magnesium lab, we
burned magnesium and after it’s
chemical change the result was
magnesium oxide. It was no longer
metal!!

8. Observing Chemical Change
• During a chemical change you
have:
– Reactants: the substance that is being
changed.
– Products: the new substance formed as
a result of the chemical reaction.

9. Observing Chemical Change
• REMEMBER: in order for a chemical
reaction to have occurred- bonds
must be broken and new bonds
must be made!!!

10. Observing Chemical Change
• EVIDENCE that a CHEMICAL
REACTION has occurred:
– Change in properties
– Change in energy

11. Observing Chemical Change
• Change in properties: color change,
a solid forms (precipitate), formation
of gas, and texture change.
• CAUTION!! Sometimes physical
changes make it SEEM like a
chemical change has occurred.
Really THINK about the changes.

12. Observing Chemical Change
• Change in Energy: During chemical
changes, energy is either absorbed
or released.
– Endothermic reactions (heat enters)
– Exothermic reactions (heat exits)
• (remember those words…??)

13. Describing Chemical Changes
• Chemical equations are used to
show/explain a chemical reaction.
– This shows the reactants and products
of a reaction
– They show the substances you start
with, on the left and the new
substances on the right separated by
an arrow.

14. Describing Chemical Changes
• Generic formula looks like:
Reactant + Reactant ---> Product + Product

15. Conservation of Mass (matter)
• During Chemical reactions, atoms
cannot be created OR destroyed.
• The total mass of the reactants must
equal the total mass of the
products.

16. Conservation of Mass (matter)
• In a chemical reaction, the number
of atoms stays the same- they are
just rearranged. Therefore, the
number of atoms in the reactants
are the same as the number of
atoms in the products.

17. Open and Closed System
• Sometimes it’s hard to understand
where the matter comes from in a
reaction.
• Matter can either come from an…
– Open System
or a…
– Closed System

18. Open and Closed System
• Open System: Matter can enter from
or exit into the surroundings during a
reaction.
• Closed System: Matter cannot enter
or leave during the reaction.