10/8/2014
Word Equations
• A “word equation” represents a chemical reaction using
words. Anything on the left side of the arrow is called a
reactant and anything on the right side of the arrow is
called a product. The arrow itself indicates a chemical
reaction has taken place.
• Example One:
“produces or yields”
Magnesium
+
Reactants
Oxygen 
Magnesium Oxide
Product
Example Two:
Sodium + Water  Sodium Hydroxide + Hydrogen Gas
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10/8/2014
The Law of Conservation of Mass
• In a chemical reaction: “the total mass of the reactants is
always equal to the total mass of the products” OR “matter
cannot be created or destroyed, just rearranged”.
• For example, when a log burns it appears to lose mass (the
log gets smaller). Where does the missing mass go?
Log + Fire  Ashes + (Heat, Water, Carbon Dioxide)
Balancing Chemical Equations
• Remember that a “word equation” shows the reactants and products
separated by an arrow and uses words. A “chemical equation” shows
the same things except it uses chemical symbols or formulae.
• Example:
Word Equation
Iron (II) + Oxygen Gas  Iron (II) Oxide
Chemical Equation
Fe (II) + O2  FeO
Does the above chemical equation obey the law of conservation of mass?
• NO! There are two oxygen atoms on the reactant side but
only one oxygen atom on the product side. This type of
chemical equation is “unbalanced” and is called a “skeletal
equation”. To make this a “balanced chemical equation” we
put coefficients (whole numbers) in front of the chemical
symbol or formula.
Balanced Chemical Equation
2Fe (II) + O2  2FeO
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