Big Idea 9:
Changes in Matter
Law of conservation of mass, physical
and chemical changes, and effects on
chemical changes
• SC.8.P.9.1
Explore the Law of Conservation of Mass by
demonstrating and concluding that mass is
conserved when substances undergo physical
and chemical changes.
• SC.8.P.9.2
Differentiate between physical changes and
chemical changes.
• SC.8.P.9.3
Investigate and describe how temperature
influences chemical changes.
Physical Changes
•
If an object/substance goes
through a physical change, it
means one of its physical
properties (see Big Idea 8) has
been affected. For example, if
you have a bottle of water
and place it in the freezer,
over time the water inside the
bottle will turn into a solid.
The frozen water in the bottle
is still water, it is just in
another phase. If you warm
that bottle up, you will have
liquid in the bottle just as you
started off with.
•
The key to recognizing a
physical change is that the
change can be reversed and
the original substance can
return to its original shape
and size. When a substance
goes through a phase change
(freezing/melting,
boiling/condensation,
sublimation), it is considered
to have gone through a
physical change.
Chemical Changes
• Chemical changes alter
the structure of the
substance and create
new substances with
different properties than
the original.
Flammability, for
example, is a chemical
property. If a piece of
paper burns, there is no
way to take the ashes
and the smoke that
escaped, put it back
together, and get the
original piece of paper
back.
• Unlike physical changes,
the key to recognizing a
chemical change, is
knowing that the
original substance
cannot be brought back
after the change has
occurred.
HELPFUL LINKS:
• http://www.chem4kids.com/files/m
atter_chemphys.html
• See Big Idea 8 – 8th grade
Law of Conservation of Mass
Whether a substance goes through a physical or
chemical change, the Law of Conservation of Mass
always exists.
Law of Conservation of Mass
• The Law of Conservation of Mass simply states that when a
substance goes through a change, the mass of the substance
before will always equal the mass of the products after the
reaction.
• The volume may change, but the mass shall remain the
same. The mass of an ice cube should equal the mass of the
liquid water after it melts.
• In order to prove this law, the physical or chemical reaction
must be conducted in a closed system. In a closed system,
interference with outside sources can be eliminated.
HELPFUL LINK:
http://homepage.mac.com/sklemmer/Essentials%20I/co
servationlab.htm
Knowledge Check
1. Explain the difference between a physical and chemical change.
2. Give an example of both a physical and chemical change.
3. State the Law of Conservation of Mass.
4. Give an example which follows the Law of Conservation of Mass.
Knowledge Check
1. Explain the difference between a physical and chemical change.
•
•
Physical – can return the object back to its original state.
A new substance with different properties is created
2. Give an example of both a physical and chemical change.
• Physical change= freezing, melting, boiling, etc..
• Chemical change = flammability, reactivity to acids
3. State the Law of Conservation of Mass.
• Mass cannot be created or destroyed; it just changes form or is
transferred to another object.
4. Give an example which follows the Law of Conservation of Mass.
•If you have 10g of liquid water and you freeze it, the ice cube will
have a mass of 10g.