1/29/2015
Unit 3 Lesson 3 Physical and Chemical Changes
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Unit 3 Lesson 3 Physical and Chemical Changes
Change of Appearance
What are physical changes of matter?
• A physical change is a change that affects one
or more physical properties of a substance.
• The appearance, shape, or size of a substance
may be altered during a physical change.
• Physical changes do not change the chemical
identity of a substance.
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1/29/2015
Unit 3 Lesson 3 Physical and Chemical Changes
Change from the Inside
What are chemical changes of matter?
• A chemical change is the process by which
one or more substances change into entirely new
substances with different properties.
• A chemical change is not the same as a
chemical property.
• Burning is a chemical change; flammability is a
chemical property.
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Unit 3 Lesson 3 Physical and Chemical Changes
What are chemical changes of matter?
• A chemical change takes place when the particles
and chemical bonds that make up a substance are
rearranged.
• Chemical changes often are influenced by
temperature.
• At higher temperatures, particles have more
average kinetic energy and rearrange more easily.
Chemical reactions often happen more quickly.
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1/29/2015
Unit 3 Lesson 3 Physical and Chemical Changes
Look for the Signs
How can you tell a chemical change has
happened?
• There are several signs that a chemical reaction
has occurred.
• Observing two or more of these signs during a
change means that you likely are observing a
chemical change.
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Unit 3 Lesson 3 Physical and Chemical Changes
How can you tell a chemical change has
happened?
• Some chemical changes produce odors, which
are caused by the formation of a new substance.
• Other chemical changes cause fizzing and
foaming, which indicate the production of gas.
• It is important to note that some physical
changes, such as boiling, produce gas bubbles.
• The only way to know if a chemical change has
taken place is to identify new substances.
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1/29/2015
Unit 3 Lesson 3 Physical and Chemical Changes
How can you tell a chemical change has
happened?
• Chemical changes may result in products in
different physical states. Liquids sometimes
combine to form a solid called a precipitate.
• Chemical changes can cause energy to change
from one form to another, such as from chemical
energy to heat and light energy.
• A change in temperature or color is often an
indication of a chemical change.
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Unit 3 Lesson 3 Physical and Chemical Changes
Conservation Is the Law
What happens to energy and mass
during physical and chemical changes?
• During a physical change, mass does not change.
Most physical changes can be reversed.
• During a chemical change, matter can seem to
vanish or to appear out of nowhere.
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1/29/2015
Unit 3 Lesson 3 Physical and Chemical Changes
What happens to energy and mass
during physical and chemical changes?
• The French chemist Antoine Lavoisier completed
experiments in sealed glass bulbs to demonstrate
conservation of mass during a reaction.
• The law of conservation of mass states that in
ordinary chemical and physical changes, mass is
not created or destroyed. It only is transformed
into different substances.
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Unit 3 Lesson 3 Physical and Chemical Changes
What happens to energy and mass
during physical and chemical changes?
• Ordinary physical and chemical changes also
follow the law of conservation of energy.
• The law of conservation of energy states that
energy cannot be created or destroyed. It only
can change from one form to another.
• Energy can be absorbed or released during
physical and chemical changes.
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Unit 3 Lesson 3 Physical and Chemical Changes
What happens to energy and mass
during physical and chemical changes?
• Changes that absorb energy are called
endothermic.
• Changes that release energy are called
exothermic.
• During a physical or chemical change, the total
amount of energy in the substances and their
surroundings remains constant.
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