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Chemical Reactions
• Fireworks are a result of
chemical reactions
Chemical Reactions
• Chemical Reactions form new
substances by breaking and
making chemical bonds
• Chemical reactions change the
way the atoms are arranged
Difference between
Physical and Chemical
Changes
• Physical
• A change in the
state
• Solid to liquid
• Liquid to gas
• Gas to liquid
• Atoms/molecules
of the
substances do
not change
• Chemical
• Atoms/molecules
broken down or
combined to
form new
substances
• Properties of
new substances
are different
than properties
of the
substances that
make them up
Reactants and Products
• Reactants: present at the beginning
of the reaction
• Products: are the substances formed
by the chemical reaction
• Example burning natural gas
• CH4+ 2O2> CO2+2H2O
• Reactants > Products
Evidence of Chemical
Reactions
• Color Change
• Formation of Precipitate
(solid formed from two
liquids)
• Formation of gas
• Temperature change:
endothermic (temp down)
exothermic (temp up)
• Change in smell
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Classification of
Chemical Reactions
• Synthesis: a
new compound
is formed by the
combination of
simpler
reactants
• Smog formed
when nitrogen
and oxygen
combine
• N2+2O2> 2 NO2
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