3. 3
occurs when the substance changes state
but does not change its chemical
composition.
For example: water freezing into ice,
cutting a piece of wood into smaller pieces,
etc.
The form or appearance has changed,
but the properties of that substance are
the same
(i.e. it has the same melting point, boiling
point, chemical composition, etc.)
4. 4
• Melting point
• Boiling point
• Vapor pressure
• Color
• State of
matter
• Density
• Electrical
conductivity
• Solubility
• Adsorption to a
surface
• Hardness
5. 5
Physical Changes
When you step on a can and crush it,
you have forced a physical change.
The shape of the object has changed.
It wasn't a change in the state of
matter, but something changed.
8. 8
Chemical Changes
A chemical change
involves one or more
substances changing
into a new
substance.
When iron (Fe) rusts
you can see it
happen.
The actual molecules
have changed their
structure (the iron
9. 9
occurs when a substance changes into something
new.
This occurs due to heating, chemical reaction,
etc.
You can tell a chemical change has occurred if
the density, melting point or freezing point of the
original substance changes.
Many common signs of a chemical change can be
seen (bubbles forming, mass changed, etc).
10. 10
• Reaction with
acids
• Reaction with
bases (alkalis)
• Reaction with
oxygen
(combustion)
• Reaction with
other elements
• Decomposition
into simpler
substances
• Corrosion
11. 11
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
chemical reaction), the composition of
matter always changes.
12. 12
Chemical Reactions are…
• When one or more substances are
changed into new substances.
• Reactants- the stuff you start with
• Products- what you make
• The products will have NEW
PROPERTIES different from the
reactants you started with
• Arrow points from the reactants to
the new products
13. Recognizing Chemical Changes
Energy is absorbed or released
(temperature changes hotter or colder)
Gas production (bubbling, fizzing, or odor
change; smoke)
formation of a precipitate - a solid that
separates from solution (won’t dissolve)
Irreversibility - not easily reversed
But, there are examples of these that are
not chemical – boiling water bubbles, etc
13
.
14. 14
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?
• Can be reversible, or irreversible
• Chemical change - a change where a
new form of matter is formed.
– Rust, burn, decompose, ferment
