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Energy and Reactions
1. Energy
What is energy?
Energy = ability to do work
What is work?
Work = TRANSFER of energy from
one object to another.
1. Energy
Energy exists in many forms
-
Kinetic
Potential
Thermal/Heat
Chemical
Electrical
Electromagnetic/Light
Mechanical
Nuclear
Sound
1. Energy
IMPORTANT
Energy CANNOT be created or destroyed
1. Energy
IMPORTANT
Energy CANNOT be created or destroyed
Energy is CONVERTED from one form to another.
1. Energy
IMPORTANT
Energy CANNOT be created or destroyed
Energy is CONVERTED from one form to another.
1. Energy
IMPORTANT
Energy CANNOT be created or destroyed
Energy is CONVERTED from one form to another.
1. Energy
IMPORTANT
Energy CANNOT be created or destroyed
Energy is CONVERTED from one form to another.
1. Energy
In this class: changes in bond energy in reactions
and physical changes
1. Energy
1. Explain the conservation of energy
2. Why might a one-step energy conversion be preferred
over a two-step conversion?
2. Physical vs Chemical Changes
2. Physical Changes and Reactions
How is a physical change different from a chemical
change?
Physical
Changing outfits
Chemical
Example:
Changing DNA
2. Physical Changes and Reactions
Signs of a chemical change
1. Evolution of a gas
2. Formation of something solid
3. Change in appearance
4. Change in energy
2. Physical Changes and Reactions
Both physical and chemical changes need energy or release
energy
Add energy to ice = water
Ice melts = water and releases energy
2. Physical Changes and Reactions
Both physical and chemical changes need energy or release
energy
Add energy to match
Match burns = releases energy as fire
2. Physical Changes and Reactions
Endothermic
absorbs/needs energy
Exothermic
releases energy
2. Physical Changes and Reactions
Show chemical changes with equations
Reactants  Products

means “produces”
2. Physical Changes and Reactions
Writing Reactions
Baking soda, NaHCO3 combines with acetic acid,
HC2H3O2 to produce sodium acetate NaC2H3O2, carbon
dioxide
CO2, and water H2O.
Page 266 # 1,3,4,5,9,10,11,12
3. Types of Reactions
5 main categories
Synthesis
Decomposition
Combustion
Single Replacement
Double Replacement
3. Types of Reactions
Combustion
Explanation: something with carbon
+ oxygen 
Example: C6H12O6 + 6O2  6CO2 + 6H2O
Pattern: Carbon + O2  CO2 + H2O
3. Types of Reactions
Synthesis
Explanation: when two or more
become one
Example: H2 + O2  2H2O
Pattern: A + B  AB
3. Types of Reactions
Decomposition
Explanation: when one becomes two
or more/breakup
Example: 2H2O  H2 + O2
Pattern: AB  A + B
3. Types of Reactions
Single Replacement
Explanation: Love Triangle
Example: Zn + CuSO4  Cu + ZnSO4
Pattern: A + BC  B + AC
3. Types of Reactions
Double Replacement
Explanation: Soap Opera Drama
Example:KCl+ NaNO2  NaCl + KNO2
Pattern: AB + CD  AD + BC
4. Balancing Reactions
OBJECTIVE:
Applying
Conservation of Mass
to Reactions
4. Balancing Reactions
Conservation of Mass:
cannot create or destroy mass
this means:
there needs to be the same
number of atoms on both sides
of reaction
4. Balancing Reactions
frame + wheels + chain + handlebars + pedals  1 bicycle
1 frame + 2 wheels + 1 chain + 1 handlebar + 2 pedals  1bicycle
What are those numbers?
COEFFICIENTS
4. Balancing Reactions
H 2 + O 2  H 2O
4. Balancing Reactions
H2 + O2  2H2O
4. Balancing Reactions
2H2 + O2  2H2O
4. Balancing Reactions
2H2 + O2  2H2O
NEVER change subscripts
4. Balancing Reactions
2H2 + O2  2H2O
CH4 + 2O2  CO2 + 2H2O
Cu + 2AgNO3  2Ag + Cu(NO3)2
2KI + Pb(NO3)2  PbI2 + 2KNO3
What are those numbers?
COEFFICIENTS
4. Balancing Reactions
Strategy for Balancing Reactions
1. Start with compound
2. Add coefficients to balance
3. Leave single elements, like O2, H2, Al, Cu, etc. for
last.
4. Use fractions if necessary.
5. Simplify if necessary. If fractions used, simplify
fractions as well.
6. Check work.
NEVER CHANGE SUBSCRIPTS!
DO NOT SPLIT COMPOUNDS!
A) Identify type of rxn B) Balance
1. Na + O2  Na2O2
2. Al + S8  Al2S3
3. O2 + C6H12O6  CO2 + H2O
4. Na + NaNO3  Na2O + N2
5. H3PO4 + KOH  K3PO4 + H2O
6. NH3 + O2  N2 + H2O
4. Balancing Reactions
Balancing Reactions with Polyatomic Ions
Mg + OH  Mg(OH)2
HgCl2 + AgNO3  Hg(NO3)2 +AgCl
Al + Hg(CH3COO)2  Al(CH3COO)3 + Hg
A) Identify type of rxn
B) Balance
1. C2H6 + O2  CO2 + H2O
2. Al + HAsO3  H2 + Al(AsO3)
3
3. H3PO4 + Mg(OH)
2
2
 Mg3 (PO4)
+ H2O
4. NH4OH + H3PO4  (NH4)3PO4 + H2O
5. Al(OH)3 + H2SO4  Al2(SO4)3 + H2O
6. C10H22 + O2  CO2 + H2O (fractions?)
4. Balancing Reactions
How are coefficients different from subscripts?
2H2 + O2  2H2O
subscripts = # of atoms
4. Balancing Reactions
How are coefficients different from subscripts?
2H2 + O2  2H2O
coefficients = how many
4. Balancing Reactions
2H2 + O2  2H2O
subscripts = # of atoms
coefficients = how many
4. Balancing Reactions
H2 + O2  H2O2
subscripts = # of atoms
coefficients = how many
End of Chapter 8
Topics Covered
1. Energy
2. Physical vs. Chemical Changes
3. Types of Reactions
4. Balancing Reactions
Sample Problem
Methane, CH4, reacts with O2 to combust and produce the
following: CO2 and H2O. This reaction results in the
release of a large amount of energy.
1. Write a balanced reaction.
2. This is what type of reaction?
3. This reaction resulted in 49.1 grams of CO2. This is
equal to how many moles?
4. CH4 is a covalent compound. Draw its Lewis Structure