Law of Conservation of Mass
In a chemical reaction the MASS of the REACTANTS must equal the MASS of the PRODUCTS.
This law is governed partially by the First Law of Thermodynamics which states that matter cannot be
created or destroyed, It can only be changed or transformed.
Writing Word Equations
A Word Equation is only one of the ways that you represent a chemical reaction. It tells you what the
reactants are
And what is produced.
Word Equations will always have the Reactants on the left side of the formula and the products on the
right.
ALL REACTANTS (Added together)

PRODUCTS (Added Together)
Zinc + Hydrochloric Acid  Zinc Chloride+ Hydrogen Gas
Potassium Iodide + Silver Nitrate  Silver Iodide + Potassium Nitrate
Water  Hydrogen Gas +
Oxygen Gas
Writing Skeleton Equations
Is a representation of a chemical reaction in which the formulas of the reactants are
connected to the formulas of the products by an arrow. Using the word equation we
replace each name with a formula:
EXAMPLES:
Word Equation 1
Methane gas + Oxygen gas  Carbon Dioxide + Water
Skeleton Equation
CH4 + O2  CO2 + H2O
Word Equation 2
Magnesium + Nitric Acid  Magnesium Nitrate + Hydrogen Gas
Skeleton Equation
Mg + H(NO3)  Mg(NO3) 2+ H2
Writing Balanced Equations
When writing a skeleton equation a problem arises. In looking at the reactants and products, they do not satisfy the
LAW OF CONSERVATION OF MASS.
We are unable to change the types or formulas to satisfy this Law, so we must change the NUMBER OF MOLECULES.
Word Equation 1
Magnesium + Nitric Acid  Magnesium Nitrate + Hydrogen Gas
Skeleton Equation
Mg + H(NO3)
NUMBER OF MOLECULES
of each element or
compound written as
a COEFFICIENT.
Mg
H
N
O
–
-
1
1
1
3

atom
atom
atom
atoms
Mg(NO3) 2+ H2
Mg
H
N
O
–
-
1
2
2
6
atom
atoms
atoms
atoms
Balanced Equation
1 Mg + 2 H(NO3)
Mg
H
N
O
–
-
1
2
2
6
atom
atoms
atoms
atoms

1 Mg(NO3)
Mg
H
N
O
–
-
1
2
2
6
2
+ 1 H2
atom
atoms
atoms
atoms
TYPES OF CHEMICAL
REACTIONS
CHEMICAL REACTION: A change in which a substance (or substances) is changed into one or more new substances
There are many different types of reactions, but most can be categorized into 4 (FOUR) specific groups.
SYNTHESIS
DECOMPOSITION
SINGLE DISPLACMENT
DOUBLE DISPLACEMENT
Also there are two additional reaction types we will study in our current curriculum
COMBUSTION
NEUTRALIZATION
Last, we will discover the difference between two subset reaction types
ENDOTHERMIC
EXOTHERMIC
SYNTHESIS REACTION
SYNTHESIS REACTION: A chemical reaction in which two or more elements or compounds combine to form a single
compound; also called a combination reaction.
A + B  AB
+
EXAMPLES:
2 H2 + 1 O2  2 H2O
Hydrogen gas + Oxygen gas  Water
4 Fe + 3 O2  2 Fe2O3
Iron + Oxygen gas  Iron (III) Oxide
DECOMPOSITION REACTION
DECOMPOSITION REACTION: A chemical reaction in which a compound is broken down into elements or smaller
compounds.
AB  A + B
+
EXAMPLES:
2 H2O  2 H2 + 1 O2
Water  Hydrogen Gas + Oxygen Gas
1 (NH4)(NO3)  1 N2O + 2 H2O
Ammonium nitrate 
dinitrogen monoxide + water
SINGLE DISPLACEMENT
REACTION
SINGLE DISPLACEMENT REACTION: a chemical reaction in which one element displaces, or replaces, another
element in a compound.
A + BC  AC + B
+
+
EXAMPLES:
1 Mg
+ 2 HCl  1 MgCl2 + 2 H2
Magnesium + Hydrochloric Acid  Magnesium chloride
1 Mg
+ Hydrogen gas
+ 2 Ag(NO3)  1 Mg(NO3)2 + 2 Ag
Magnesium + silver nitrate  Magnesium nitrate + silver
DOUBLE DISPLACEMENT
REACTION
DOUBLE DISPLACEMENT REACTION: a chemical reaction that occurs when elements in different compounds
displace each other or exchange places to form a new compound
AB + CD  AD + CB
+
+
EXAMPLES:
1 Pb(NO3) + 2 KI  1 PbI2 + 2 K(NO3)
Lead (II) Nitrate + Potassium Iodide  Lead (II) Iodide + Potassium Nitrate
1 Na2(CO3)
+ 1 CaCl2  2 NaCl + 1 Ca(CO3)
Sodium Carbonate + calcium chloride  Sodium Chloride + Calcium Carbonate
Combustion Reaction
COMBUSTION REACTION: a chemical reaction that occurs when a hydrocarbon reacts with oxygen to form carbon
dioxide and water. (Two types of combustion reactions – complete and incomplete).
Hydrocarbon + Oxygen  Carbon Dioxide + Water
+
+
EXAMPLES:
1 C3H8 + 5 O2  3 CO2 + 4 H2O
Propane (Tricarbon Octahydride) + Oxygen Gas Carbon Dioxide + Dihydrogen Monoxide
Neutralization Reaction
NEUTRALIZATION REACTION: a chemical reaction that occurs when an acid reacts with a base to form a t a
minimum a type of metal salt and a water.
Acid + Base  Salt + Water
+
+
EXAMPLES:
1 HCl + 1 Na(OH)  1 NaCl + 1 H2O
Hydrogen Chloride + Sodium Hydroxide  Sodium Chloride + Dihydrogen monoxide
(Hydrochloric Acid)