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Balancing Equations
Chemical Equation: a way to represent chemical reactions on
paper.
Animation
http://www.chemistry.ohio-state.edu/betha/nealChemBal/
The law of conservation of matter states matter cannot be
created or destroyed but can change from one form to
another.
Therefore, equations must be balanced!
Atoms can be neither created nor destroyed in an ordinary
chemical reaction, so there must be the same number of atoms
on both sides of the equation.
These numbers are found in a chemical equation:

Subscripts - The small numbers to the lower right
of chemical symbols. Subscripts represent the
number of atoms of each element in the molecule.
How many atoms of each element are there in one
formula unit of ammonium sulfide?
Ammonium sulfide is (NH4)2S
How many atoms of each element are there in one formula unit of barium
nitrate?
Barium nitrate is Ba(NO3)2

Coefficients - The large numbers in front of chemical formulas.
Coefficients represent the number of molecules of the substance in
the reaction.
How many atoms of each element are there in three formula units of
barium nitrate?
3Ba(NO3)2
Check for Diatomic Molecules - H2 - N2 - O2 - F2 - Cl2 - Br2 - I2
If these elements appear by themselves in an equation, they
must be written with the subscript 2
Please write these diatomic molecules on you blue ion sheet.
Chemical equations give information in two major areas.
First they tell us what substances are reacting and what substances are
being produced.
Reactants  Products
2H2 + O2  2H2O
What are the reactants?
What are the products?
Second, the coefficients of a balanced equation tell us in what ratio MOLE
the substances react or are produced.
2H2 + O2  2H2O
How many moles of water are produced?
How many moles of hydrogen are needed?
How many moles of oxygen are needed?
How do we balance equations?
Balance equations by changing coefficients
Never by changing formula subscripts
Steps:
1. Write all reactants on the left and all products on the right side of the
equation arrow. Make sure you write the correct formula for each
element.
2. Use coefficients in front of each formula to balance the number of
atoms on each side.
3. Multiply the coefficient of each element by the subscript of the
element to count the atoms. Then list the number of atoms of each
element on each side.
4. It is often easiest to start balancing with an element that appears only
once on each side of the arrow. These elements must have the same
coefficient. Next balance elements that appear only once on each
side but have different numbers of atoms. Finally balance elements
that are in two formulas in the same side.
Balance these equations:
_____Zn + ______HCl  _____ZnCl2 + _____H2
_____KClO3  _____KCl + _____O2
_____S8 + _____F2  _____SF6
_____Fe + _____O2  _____Fe2O3
_____C2H6 + _____O2  _____CO2 + _____H2O
More Practice
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