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“Matter
and
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KINDS of Change
There are 2 kinds of change: Physical Change
or
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Physical vs. Chemical Change
Physical change
will change the visible
appearance, without changing the
composition of the material.
–Boil, melt, cut, bend, split, crack
–Is boiled water still water?
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States of matter
(property or change?)1) Solid- matter that can not flow (definite shape) and has definite volume.
2) Liquid- definite volume but takes the shape of its container (flows).
3) Gas- a substance without definite volume or shape and can flow.
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Solid
Liquid
Gas
Melt Evaporate
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8
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Physical vs. Chemical Change
Chemical change
- a change where a
new form of matter is formed.
–Rust, burn, decompose, ferment
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Elements vs. Compounds
Compounds
can
be broken down
into simpler substances by
chemical means, but elements
cannot
.
A “
chemical change
” is a change
that produces matter with a
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Evidence of Chemical Change
in order to be absolutely sure that a chemical
reaction has taken
place, you need to go down to the molecular level and analyze the structures of the
molecules at the beginning and end
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Evidence of Chemical Reactions
look for evidence of a new substance
visual clues (permanent) – color change
– precipitate formation
» solid that forms when liquid solutions are mixed
– gas bubbles
– large energy changes
» container becomes very hot or cold » emission of light
other clues – new odor
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Evidence of Chemical Change
Color Change
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Chemical Change
A change in which one or more
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Properties of Compounds
Quite different properties than their
component elements.
Due to a CHEMICAL CHANGE, the
resulting compound has new and
different properties:
• Table sugar – carbon, hydrogen,
oxygen
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Chemical Changes
The
ability
of a substance to undergo
a specific chemical change is called a
chemical
property
.
• iron plus oxygen forms rust, so the
ability to rust is a chemical property
of iron
During a chemical change (also called
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worksheet.
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The Law of
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We’ve talked about
changes in matter…
The evaporation of a puddle
of water
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HOWEVER…
No matter is
created or
destroyed by such changes!
The total
amount of
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How did scientists come up
with this law?
They measured the mass of
the reactants (vinegar and baking soda) and then, after the reaction took place, they measured the mass of the
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- Page 55
reactants = product
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The Law of
Conservation of Mass
During a chemical reaction, matter
cannot be created or destroyed.
Even though the matter may change
from one form to another, the same number of atoms exists before and
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Since the overall mass of the
matter does not change…
The mass of the reactants – the
substances there before the
reaction occurs – must equal the mass of the product – the
substances there after the reaction takes place.
Mass of
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The Formation of Rust
Iron
– Hard, gray-colored metal
Rust
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When iron reacts with oxygen
in the air, they form rust or
IRON OXIDE.
This is written as:
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Fe Fe
Fe Fe
O2
O2 O2
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Conservation of Mass
During any chemical reaction, the
mass of the products is always equal
to the mass of the reactants.
All the mass can be accounted for:
–Burning of wood results in products
that appear to have less mass as
ashes; where is the rest?
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Evidence of Chemical Reactions
look for evidence of a new substance permanent visual clues:
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Evidence of Chemical Reactions
look for evidence of a new substance
permanent visual clues: 1. color change
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Evidence of Chemical Reactions
look for evidence of a new substance
permanent visual clues: 1. color change
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Evidence of Chemical Reactions
look for evidence of a new substance
permanent visual clues: 1. color change
2. precipitate formation 3. gas bubbles
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Recognizing Chemical Changes
1) Energy is absorbed or released
(temperature changes hotter or colder)
2) Color changes
3) Gas production (bubbling, fizzing, or odor change; smoke)
4) formation of a precipitate - a solid that separates from solution (won’t dissolve)
5) Irreversibility - not easily reversed
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Gas tests
What are the four GASES
