Law of Conservation of
Matter:

Matter cannot be created or
destroyed.
AMOUNT OF REACTANTS =
AMOUNT OF PRODUCTS ! ! ! !
Guidelines for Balancing
Chemical Equations:

 1) Do NOT change the subscripts !
 2) Every element MUST have the same amount of atoms
on both sides of the equation.
 3) Add stoichiometric coefficients (numbers) in front of
the chemical formula.
Guidelines (cont.)

 4) Once a coefficient is added, go back and check the
rest of the equation.
 5) Leave hydrogens and oxygens to last. Balance
hydrogens with an even number.
 6) CHECK EQUATION TO BE SURE EVERYTHING
BALANCES/CANCELS OUT ON BOTH SIDES ! ! !
Diatomic elements

 Bromine (Br2)
 Chlorine (Cl2)
 Fluorine (F2)
 Hydrogen (H2)
 Iodine (I2)
 Nitrogen (N2)
 Oxygen (O2)
Helpful Hints

 Balances metals and then nonmetals.
 Elements found in only ONE compound on each side—balance
first
 Polyatomic ions usually stay together—balance as a unit.
 Elements in diatomic state? Balance compounds with these
elements using an EVEN number
 Do not be afraid to use FRACTIONS as coefficients !!
 Use common multiplier and multiply all coefficients to get rid of the
fraction
Example 1:

KI (aq) +
Pb(NO3)2 
KNO3 +
PbI2
Example 2:

C2H6
+
O2 
CO2
+
H2O
Practice

1) FeI3 +
K2SO4 
KI +
Fe2(SO4)3
2) CaSO4 + Al(NO3)3  Ca(NO3)2 + Al2(SO4)3
Telling a story….

Writing Chemical
Equations

1) Identify reactants, write chemical formulas.
1) Identify products, write chemical formulas.
3) Write the complete chemical equation.
4) Balance the equation.
Example 1:

Merry and Pippin find lead (II) chloride
and lithium sulfate in Gandalf’s chemical
supply cabinet. They combine these
chemical compounds and then run to
Gandalf so he may identify the produced
chemical compounds. Gandalf identifies
the compounds as lead (II) sulfate and
lithium chloride.
Example 2:

A chemist at a Wake Forest chemistry
lab prepares a potassium bromide
solution dissolved in water to react
with chlorine gas. This reaction
produces bromine in the liquid state
and potassium chloride in solution.
Example 3:

 Merry and Pippin have gotten in over their heads
AGAIN!! Without Gandalf, they have combined a
liquid phosphorus-chlorine compound which is
77.45% Cl by mass with water. Gandalf hears the
commotion and immediately returns to identify an
aqueous solution of phosphoric acid and
hydrochloric acid.
Homework

 Balancing Equations Worksheet