Changes of Matter
Chapter 2
Notation in Chemistry
∆  change
Pronounced “delta”
EX: ∆T = change in temperature
Physical Changes in Matter
• A physical change occurs when a substance
undergoes a change that does not alter its
chemical composition.
S
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t
• Physical changes can be reversible or
irreversible.
• Examples of physical changes:
• Changes of state/phase
• Dissolving
• Cutting, Tearing, Grinding, Reshaping, etc.
H2O & NaCl
Phase Changes
Chemical Changes in Matter
• Chemical changes occur when a substance
undergoes a change that chemically alters the
composition of that substance.
• After a chemical change, completely new
substances with new properties are formed.
• Examples of Chemical Changes:
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•
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Burning
Scorching
Cooking
Fermenting
Decomposing
Evidence of a Chemical Change (Reaction)
1) Change in Temperature (∆T)
2) Change in Color
3) Evolution/Formation of a Gas
(effervescence)
4) Production of Light
5) Production of a Precipitate
* NOT ALWAYS A SIGN OF A CHEMICAL REACTION… true indicator, test composition*
Law of Conservation
• All chemical changes are governed by a scientific law.
• The law of conservation states, “mass/matter/energy
cannot be created or destroyed during a normal
chemical reaction”.
Combine the two reactants