Chemical Equations, Word
Equations and Balancing
• THE MEANING OF A CHEMICAL
EQUATION
• A chemical equation is a chemist’s shorthand
expression for describing a chemical change.
As an example, consider what takes place
when iron rusts.
Example
• Fe + O2 → Fe2O3
• In this expression, the symbols and formulas of the
reacting substances, called the reactants, are written
on the left side of the arrow and the products of the
reaction are written on the right side. The arrow is
read as “gives”, “yields”, or “forms” and the plus (+)
sign is read as “and”. When the plus (+) sign appears
between the formulas for two reactants, it can be
read as reacts with. (The + sign does not imply
mathematical addition). The equation, above, can be
read as iron reacts with oxygen to yield (or form)
iron(III) oxide.
Word Equation
• The same set up but the full name
instead of chemical formula
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Fe + O2 → Fe2O3
SO it would be:
Iron (s) + Oxygen (g) → iron(III)oxide (s)
The word equation often includes the state of
matter (s)(l)(g)(aq)-aqueous solution
Law of Conservation of Mass
• The mass of the reactants equals the
mass of the products.
• Sodium and oxygen react to create sodium oxide
• Na + O2  Na2O (THIS DOES NOT HAVE THE
SAME MASS)
• Balanced:
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4 Na + O2  2 Na2O
4 Na
- 4 Na
2O
-2O
NOW IT IS BALANCED
Balancing
• From the word equation write a skeleton
equation (unbalanced)
• Then count the number of atoms of
each element and match the number on
the reactant side with the number on the
product side.
Examples
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Balance these equations:
___Cl2 + __ NaBr  __ NaCl + __Br2
__ Ag2O  __ Ag + ___O2
__Mg + ___ HCl  __H2 + __MgCl2
___ H2 + __O2  __ H2O
__Cl2 + __ NaBr  __ NaCl + __Br2
Answers
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Cl2 + 2 NaBr  2 NaCl + Br2
2 Ag2O  4 Ag + O2
Mg + 2 HCl  H2 + MgCl2
2 H 2 + O 2  2 H 2O
Cl2 + 2 NaBr  2 NaCl + Br2