Chemical vs. Physical
Changes
Physical Changes, P. 68-72
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Physical changes involve
altering the form of a
substance, but does not
change it to another
substance.
Ex: bending a nail, tearing
paper, making playdough
changing states of matter –
boiling water, freezing
popsicle, mixing koolaid, etc…
Chemical Changes Defined
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During a chemical change,
matter is changed into a new
substance with new properties.
Ex: burning wood – wood to
ash and gases
Other examples: baking a
cake, glow sticks, making toast,
mixing vinegar and baking
soda, milk ‘curdling’, etc…
Think of a chemical change of
when you can’t change the new
substance back to it’s original
form.
Law of Conservation of Matter
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Matter is not created or destroyed in any chemical or
physical change.
Mass of reactants always equals the mass of the
products
Energy and Change
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During physical and chemical changes,
energy is either added or taken away.
Thermal energy is energy from molecule
movement (heat)
Chemical energy is the energy from the
bonds between molecules in a substance.
Law of conservation of energy – during any
chem. Or phys. Change, amount of energy
stays the same.
Examples of conservation of
Energy
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Unlit match contains
chemical energy
When lit – energy
converted to thermal and
light energy.
Amount of energy
remains the same, just
changes form.
Changes of State
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All changes of state are physical changes.
All state changes involve loss or gain of thermal
energy
Liquid to Gas State
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Vaporization is when a
liquid gains enough thermal
energy to become a gas –
molecules move faster.
Evaporation – vaporization
only occurs on the surface.
Ex: puddle drying up after a
rain.
Boiling – when vaporization
happens throughout the
liquid.
Condensation
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When a gas loses enough
thermal energy to return to a
liquid, called condensation.
Molecules slow down
Ex: dew on grass in the
morning.
Clouds = water vapor cools
at higher elevations,
becomes liquid water.
Sublimation
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Sublimation occurs when the
surface particles of a solid gain
enough energy to become a
gas.
Skip the liquid state.
Ex: Dry ice – solid carbon
dioxide.
Dry ice made by putting carbon
dioxide under extreme
pressure, when reaches normal
pressure, sublimates.
Chemical Changes
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Chemical changes = chemical reactions
In all chemical reactions, new substances are
produced.
All reactions either release or absorb energy.
Ex: of absorption – plant growth, cold packs.
Ex: of release – digestion, baking, lighting a
match, burning wood