Balancing and
Chemical Reactions
Why do we have to Balance
equations?
• Hint: Think about Law of Conservation
of Mass!
• The # of atoms of each element must
be equal on both sides of the equation.
Parts of a Chemical Equation
• Parts of a Chemical Formula
Chemical formula is a math formula for science!
Label the different parts?
2Na + Cl2 2NaCl
Reactants=Left side of equation
“and”
Products=Right side of Equation
“yields, produces, forms”
Same as an = sign
Coefficient-used to balance a
chemical equation
Subscript-determines how
many atoms of an element
are needed for the compound
Vocabulary Continued
3) Catalyst - substance that changes the
rate of a chemical reaction but remains
unchanged throughout the reaction
Symbols
(s)
(l)
(g)
(aq)
Pt
Yields: indicates result of reaction
Reversible reaction
Indicates a precipitate (solid)
Indicates a gaseous product
Reactant or product in a solid state
Reactant or product in a liquid state
Reactant or product in a gaseous state
Reactant or product in a aqueous state
Reactants are heated
Presence of a catalyst
Steps to Balance an
Equation
• Step 1: List all the elements in the equation
underneath the center of the equation
• Step 2: Count how many of each element is
on the reactant side then the product side
• Step 3: Is this balanced or unbalanced
• Step 4: balance the equation if necessary
by adding coefficients
Practice
• _____ N2 + _____ H2 → _____NH3
N
H
• _____ KClO3 → _____ KCl + _____ O2
K
Cl
O
__ FeCl3 + __ NaOH → __ Fe(OH)3 + __ NaCl
___ Na + ___ H2O → ___ NaOH + ___ H2
__ C2H6 + __ O2  __ CO2 + __ H2O
__ AlBr3 + __ K2SO4 → __ KBr + __ Al2(SO4)3
Types of Reactions
Notes
Reduction-Oxidation
Reactions (REDOX)
• Reduction-Oxidation Reactions: any
chemical reaction where elements undergo
changes in oxidation number (charges)
• How can I tell if this is REDOX or not?
– Elements that are NOT in a compound will
have a charge of ZERO.
– Elements in compounds will have a CHARGE
REDOX Vocabulary
1) Reduced: the oxidation state (charge) of
the element decreases from the reactants
to the products
2) Oxidized: the oxidation state (charge) of
the element increases from the reactants
to products
Redox Reactions? Y OR N
• NaCl + F2  NaF + Cl2
• P + O2  P2O5
• FeCl3 + NaOH  Fe(OH)3 + NaCl
• Ag2O  Ag + O2
• S8 + O2  SO3
Precipitate Reactions
• These are reactions where all of the pieces
are rearranged from reactants to products and
we get a precipitate (solid ) out.
• Examples:
__ Al2(SO4)3 + __ K3PO4__ K2SO4 + __ AlPO4
__ FeCl3 + __ NaOH  __ Fe(OH)3+ __NaCl
Precipitate Vocabulary
1) Precipitate: solid produced within a
solution as a result of a chemical reaction
2) Aqueous solution: a solution where the
solvent is water
Acid/Base Reactions
• This type of reaction involves an acid (a
compound that starts with H) and a base (a
compound that ends with an –OH) that make
a salt and water.
• Examples:
___Ca(OH)2 + ___HCl  ___CaCl2 + ___H2O
___H2SO4 + __NaOH  + __H2O + __Na2SO4
Energy in Reactions
Endothermic vs. Exothermic
• EndothermicEnergy moves from the surroundings into the
source
EX: Cold packs, Alka seltzer
• ExothermicEnergy moves from the source out to the
surroundings
EX: Light a match, fuel
Types of Reactions
Notes
Why do chemicals react?
• You already know!!!!!
– To fill up their outer shells…
• when we create chemical bonds we have a
chemical reaction!!
• Types:
– Ionic
– Covalent
– Metallic
Types of Reactions:
• 5 types:
– Synthesis
– Decomposition
– Single Displacement
– Double Displacement
– Combustion
Synthesis
• Two or more elements combine to
form 1 chemical compound
– EX: 2Mg + O2
2MgO
– Analogy: One girl + One Boy = One couple
• Generic equation:
A + B AB
• Another example:
Water Formation
Decomposition
• When a compound breaks into 2 elements
or simpler compounds-“break down”
– 2NaCl = 2Na + Cl2
– Analogy: One couple= One boy + one girl (Divorce)
• Generic equation:
AB A + B
• Another example: ”Electrolysis”
Decomposition
Single Displacement
• A single uncombined element replaces another in a
compound. Two reactants yield two products.
Analogy: A “playa girl” has a
boyfriend but likes a cuter boy instead
SD Animation
• Generic Example:
AB + C A + BC
Example:
Lets visualize it!
Double Displacement
• When one element of each compound
changes places with the other element
– Analogy: Two couples that switch partners
• Generic Example:
AB + CD AC + BD
• Example:
PbCl2 + Li2SO4
PbSO4 + 2LiCl
DD RX
Combustion Reaction
• What do we know as combustion?
– FIRE!!!!
– Requires a fuel and oxygen and produces CO2
and H2O
– Releases so much energy a flame is released
• Generic example:
C(x)H(x)+O2→H2O(g)+CO2(g)
Combustion Reaction
Balancing Chemical Equations
• Why do we need to balance?
– Law of Conservation of Mass-mass can
not be created or destroyed, it is only
changed to a different form
• Everything on the left has to equal everything
on the right!!!
• Just like math… 3 + 0 = 5 WRONG!!!
3 + 2 = 5 RIGHT!!!
Lets look at our equation..
2Na + Cl2 2NaCl
What did we call each part?
Word Equations
Must know the Diatomic Molecules:
Hydrogen – H2
Nitrogen – N2
Oxygen – O2
Fluorine – F2
Chlorine – Cl2
Bromine – Br2
Iodine – I2
Word Equations Practice
•
As I quoted “You cannot forget how to
write formulas!”
Practice:
1) iron (III) chloride and ammonium
hydroxide produce iron (III) hydroxide and
ammonium chloride
Word Equations Practice
2) potassium and chlorine combine to form
potassium chloride
3) ammonium nitrate yields dinitrogen
monoxide and water
4) dicarbon dihydride and oxygen produce
carbon dioxide and water
5) aluminum bromide and chlorine react to
form aluminum chloride and bromine