A physical property of matter is one that can be observed without
changing its composition. Gold is a shiny yellow metal. Lead has a
high density. Observations of these characteristics do not change the
composition.
A chemical property is one which is observed when matter
undergoes a transformation that results in a change of composition.
Gasoline will burn in air to form products which are very different
from the original material. Iron will rust in moist air to form a
compound called iron oxide. The fact that gasoline burns and iron
rusts are therefore chemical properties.
A physical change is a change in the form of matter without
changing its composition. Examples of such changes are phase
changes such as melting, boiling, etc.
A chemical change is one that leads to a change in the composition of the
matter involved. The burning of wood leads to products very different
than the starting material.
Physical changes are quite often reversible. Ice can be melted to form
liquid water; however, water can be readily reconverted to ice.
Chemical changes are usually irreversible. Gasoline can be burned to
produce water and carbon dioxide, but it is not possible to reconvert these
into the original material.
Even though matter can undergo changes it is important to realize that in
ordinary chemical reactions matter cannot be created or destroyed. We
say that matter is conserved. This is one of the fundamental conservation
laws.
PHYSICAL
CHANGE
PHYSICAL CHANGE
•Will change the visible appearance, without
changing the composition of the material.
•Can be reversible or irreversible
-boil, melt, cut, bend, split, crack
• A Physical change is a change in a
substance that does not change what the
substance is.
PHYSICAL
CHANGE
EXAMPLES
• Examples of physical change include:
– Change in shape
– Change in size
– Change in phase
• Melting (solid to liquid)
• Boiling (liquid to gas)
• Evaporation (liquid to gas)
• Condensation (gas to liquid)
• Freezing (liquid to solid)
• Sublimation (solid to gas)
• Deposition (gas to solid)
PHYSICAL CHANGE
• Physical changes
might be caused
by:
– Grinding
– Cutting
– Crushing
– Bending
– Breaking
– Heating/cool
ing
• (change
in phase)
– squishing
PHYSICAL CHANGE
• Evidence that a physical change has
occurred might include:
– Change in shape
– Change in form
– Change in size
– Change in phase (This is always a
physical change!)
– Physical changes are usually
reversible
PHYSICAL CHANGE
• What could you do to
these items to cause a
physical change to occur?
CHEMICAL
CHANGE
CHEMICAL CHANGE
• a property that can only be observed
by changing the composition of the
material.
• A chemical change is a change in
which a substance is changed into a
different substance.
(You’ve
changed what it is.)
CHEMICAL CHANGE
• Examples of chemical
changes include:
– Burning
– Rusting
– Tarnishing
– Decomposing
– Polymerization
CHEMICAL CHANGE
• Chemical changes occur
when a chemical reaction
causes bonds between
atoms to break or to form.
CHEMICAL CHANGE – CHEMICAL
REACTIONS
• There are 5 types of chemical
reactions that cause chemical
changes to occur.
CHEMICAL CHANGE – CHEMICAL
REACTIONS
1. Composition reactions
– Two things come together
to form something new
– A + B = AB
– 2H2 + O2  2H2O
CHEMICAL CHANGE – CHEMICAL
REACTIONS
2. Decomposition reactions
– 1 thing breaks apart to form 2 or more
things.
– AB = A + B
– 2H2O  2H2 + O2
CHEMICAL CHANGE – CHEMICAL
REACTIONS
3. Single replacement reactions
– One atom replaces another
atom
– A + BC = AC + B
or
A + BC = AB + C
– Mg + 2HCl  H2 + MgCl2
CHEMICAL CHANGE – CHEMICAL
REACTIONS
4. Double replacement reactions
– Two chemicals switch places
– AX + BY = AY + BX
– 2KI + Pb(NO3)2  PbI2 +
2KNO3
CHEMICAL CHANGE – CHEMICAL
REACTIONS
5. Combustion reaction
– A substance combines with
oxygen and releases energy.
– C3H8 (propane) + 5O2  3CO2
+ 4H2O
CHEMICAL CHANGE – CHEMICAL
REACTIONS
6. Acid-Base Reaction
– This is a special kind of double displacement reaction that takes
place when an acid and base react with each other. The H+ of the
acid reacts with the OH – of the base forming water.
HCl + NaOH  NaCl = H2O
CHEMICAL CHANGE: EVIDENCE
• Evidence that a chemical change
has occurred might include:
– A color change
– An odor change
– Formation of a precipitate (you
mix two liquids and make a
solid)
– Gas is formed (bubbles)
– Changes in physical properties.
PHYSICAL AND CHEMICAL CHANGE
• During a chemical change
energy can be released in
the form of:
– Heat
– Light
CHEMICAL CHANGE – CHEMICAL
REACTIONS
• When a chemical change
occurs, energy is either
released or absorbed.
PHYSICAL AND CHEMICAL CHANGE HEAT
• A chemical reaction that
releases energy in the form of
heat is called exothermic.
– Heat comes OUT
• Exo = out
• Thermic = heat
– It will feel HOT.
PHYSICAL AND CHEMICAL CHANGE HEAT
• A chemical reaction that
absorbs energy in the form
of heat is called
endothermic.
– Heat goes IN
• Endo = in
• Thermic = heat
– It will feel COLD
Classify the following as chemical change (cc),
chemical property (cp), physical change (pc),
or physical property (pp).
1 . _ _ _ _ H E AT
CONDUCTIVITY
6. ____
S H O RT E N I N G
M E LT I N G
11. _ _ _ AC I D
R E S I S TA N C E
12. ___
BRITTLENESS
2 . _ _ _ _ S I LV E R
TA R N I S H I N G
7. ____
EXPLODING
DY N A M I T E
3. ____
S U B L I M AT I O N
8. ____
COMBUSTIBLE
4. ____
M AG NETI Z I NG
STEEL
14. ___ BAKING
BREAD
9 . _ _ _ _ W AT E R
FREEZING
15. ___
BREAKING A
BONE
5. ____ LENGTH
O F M E TA L
OBJECT
1 0 . _ _ _ _ WO O D
BURNING
13. ___ MILK
SOURING