Chemical Equations
Chemistry
Mrs. Coyle
Chemical Equations:
represent chemical reactions
 Word Equations
 Skeleton Chemical Equations
 Balanced Chemical Equations
Word Equations: show the names of
the reactants and the products
Reactants

Products
Methane + Oxygen  Carbon Dioxide + Water
 The arrow (yield sign) and indicates that a
reaction took place.
Skeleton Chemical Equations
The formulas of the reactants and
products are written without indicating
their relative amounts.
Example:
CH4+ O2 CO2 +H2O
Balanced Chemical Equations
 The chemical formulas and the relative
amounts of the reactants and products are
written.
Example:
CH4 + 2O2 CO2 + 2H2O
 The coefficients indicate the relative amounts
of each substance.
 Equal number of atoms of each element must
appear on both sides of the balanced equation.
Why does a chemical reaction have to
be balanced?
 In any chemical or physical
change, mass is neither created or
destroyed
 Mass is CONSTANT
 Law of Conservation of Mass
(Antoine Lavoisier)
Combustion of Methane
CH4 + 2O2 CO2 +
Atoms are rearranged!
2H2O
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
 Word equation:
hydrogen peroxide  water + oxygen
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
 Skeleton equation:
H 2O 2

H 2O
+
O2
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
 Balanced Equation:
2H2O2

2H2O
+
O2
Example: Decomposition of hydrogen
peroxide in the presence of a catalyst.
Balanced equation showing
 the catalyst (MnO2)
 the state of the reactants and products:
MnO2
2H2O2(l)

2H2O (l)
+
O2 (g)