Cornell Notes
Topic:
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Questions Notes
REACTION ENERGY
How is energy used
in a reaction?
Energy in Reactions
Energy must be added to break
the original bonds apart to cause
a change
When bonds are formed energy
is released
–This energy is in the chemical
bonds
Energy in Reactions
Exothermic reaction – a reaction
that transfers energy from the
reactants to the surroundings
Heat “exits”
Temperature
of substance
increases
Exothermic Reactions
Energy in Reactions
Endothermic reaction – a reaction
in which energy is transferred to
the reactants from the
surroundings
Heat “enters”
Temperature of
substance decreases
Endothermic Reactions
TYPES OF REACTIONS
What are the types
of reactions?
Types of Reactions
–Synthesis– when 2 or more
substances form a new more
complex compound
–A + B
AB
–An iron bar rusts. The iron reacts with
oxygen in the air to make rust.
–4 Fe + 3 O2
2 Fe2O3
Synthesis Reaction
H
H
H
O
O
H
Types of Reactions
Decomposition reaction – when one
compounds breaks into 2 or more
products
–AB A + B
–When glucose (sugar) is broken
down by yeast it creates ethyl
alcohol and carbon dioxide gas
–C6H12O6 2 C2H5OH + 2 CO2
–Add heat or Electrolysis – using
electricity to break apart bonds
Decomposition Reaction
H
H
O
H
H
O
Types of Reactions
Single displacement – a reaction in which
atoms of one element take the place of
atoms in another compound
–AB + C
AC + B
Zn (s) + 2HCl (aq)
Single Displacement Reaction
ZnCl2 + H2 (g)
Types of Reactions
Double displacement – a reaction in
which ions exchange between 2
compounds
–AB + CD AC + BD
–An antacid (calcium hydroxide)
neutralizes stomach acid
(hydrochloric acid).
Ca(OH)2 + 2 HCl CaCl2 + 2 H2O
–Causes a gas or precipitate to form
Combustion Reactions
• In a combustion reaction, a hydrocarbon
combines with oxygen, releasing a large
amount of energy in the form of light and heat.
The products are always CO2 and H2O.
CxHx + O2
CO2 + H2O
• example: combustion of propane
C3H8(g) + 5O2(g)
3CO2(g) + 4H2O(g)
Methane Combustion