Equations & Balancing
Outline
 Word
Equations
 Skeleton Equations
 Conservation of Mass
 Balanced Chemical Equations
Chemical Equations

Represent a chemical reaction.

Are made up of two parts:
Reactants  Products

eg. methane + oxygen  carbon dioxide + water
CH4 + O2  CO2 + H2O
Chemical Equations
 Reactants
are listed on the left side
and separated by a plus sign (+).
 Products
are listed on the right side
and separated by a plus sign (+).
Word Equations
 Word
Equations – only the chemical
names of the reactants and products are
shown.
eg. methane + oxygen  carbon dioxide + water
Skeletal Equations
 Unbalanced
system where the chemical
names are converted to chemical
symbols/formulas.
 Eg.
CH4 + O2  CO2 + H20
Conservation of Mass
 Mass
of the reactants = the mass of the
products.
Why?
 Atoms are not created or destroyed in a
chemical change.
 Formulas
changed.
for molecules cannot be
Balanced Chemical Equation
 When
the reactants and products
contain equal numbers of the same
atom the chemical equation is
balanced.
 Balanced
by the use of coefficients
Balanced Chemical Equation
 Coefficients
are numbers written in
front of chemical formulas.
 They
indicate number of atoms or
molecules of that substance.
CH4 + 2O2  CO2 + 2H20
Coefficient
Balanced Chemical Equation
 Physical
state symbols are added to
show the substance’s composition
 (s) – solid



(l) – liquid
(aq) – aqueous
(g) - gas
CH4(g) + 2O2(g)  CO2(g)+ 2H20 (l)
Balancing Equations
CH4 + O2  CO2 + H20
Type of atom
(symbol)
C
H
0
# in reactants
1
4
2
# in products
1
2
3
Balancing Equations
CH4 + O2  CO2 + 2H20
Type of atom
(symbol)
# in reactants
# in products
C
1
1
H
0
4
2
4
4
Balancing Equations
CH4 + 2O2  CO2 + 2H20
Type of atom
(symbol)
# in reactants
# in products
C
1
1
H
0
4
4
4
4
Balanced Chemical Equation
General Rules
1)
2)
3)
4)
5)
Balance metals first.
Balance non-metals next (except
hydrogen and oxygen). Polyatomic ions
can be balanced as a group.
Balance hydrogen and oxygen last.
Ensure that the eqn is in lowest terms.
Check to ensure that there are the same
# of each type of atom before and after
the rxn
Balanced Chemical Equation
 Use
coefficients to change the
number of atoms of an element.
 Never
 Some
change the subscripts.
equations may take longer than
others to solve (be patient).