Balancing Equations

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Balancing Equations
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What is a chemical equation?

• When a chemical reaction occurs, it can be
  described by an equation.
• This shows the chemicals that react (called the
  reactants) on the left-hand side,
• And
• the chemicals that they produce (called the
  products) on the right-hand side.
• The chemicals can be represented by their names
  or by their chemical symbols.
• Unlike mathematical equations, the two sides are
  separated by an ARROW, that indicates that the
  reactants form the products and not the other way
  round. ( YIELD)

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Types of reactions

• SYNTHESIS 2 or more substances react to form a
  single product
• X Y ? Z
• DECOMPOSITION- a single reactant breaks down into
  2 or more products.
• A ? B C

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Types of reactions

• SINGLE REPLACEMENT one element replaces another
  in a compound such that an element combines with
  a compound to produce and element and a compound.
• X YZ ? XZ Y
• DOUBLE REPLACEMENT 2 compounds react to make 2
  different compounds
• AB CD ? AD CB

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Types of reactions

• COMBUSTION- one reactant (a fuel) combines with
  oxygen to produce an oxide and water (H2O)
• Fuel O2 ? CO2 H2O

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Aluminum Oxygen --gt Aluminum OxideAl O2 ?
Al2O3

• You can see by looking at it that there is
  something wrong with this equation.
• Al 1 Al 2
• O 2 O 3
• If you count the number of atoms of each type on
  each side, you will see that there is only one
  aluminum atom on the left side whereas there are
  two on the right.
• There are two oxygen atoms on the left side, as
  compared to three on the right side.
• This clearly doesn't match.

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Al O2 ? Al2O3

• Remember the lowered numbers are subscripts. You
  cant change those.
• The number in front is called a Coefficient. It
  multiplies everything behind it by that number.
  This is what you change to make the number of
  elements equal on both sides of arrow

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Al O2 ? Al2O3

• Pick an element that is not balanced.
• Oxygen for example.
• Al O2 ? Al2O3
• Count how many on each side 2O ? 3O
• Multiply either or both sides to make them equal
• Al 3O2 ? 2Al2O3
• 3 x 2 6 2 x 3 6
• 6 O 6 O
• You put the coefficients in the front of the
  complete formulas. This will change the number
  of the other elements in the formula also.

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Al 3O2 ? 2Al2O3

• Now do aluminum
• Count the Aluminums on each side
• 1 aluminum ? 4 Al
• 4 x 1 ? 4 Al
• 4Al 3O2 ? 2Al2O3
• 4Al 4 Al
• 6O 6O
• Balanced ?

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Law of Conservation of matter

• In a chemical reaction, Atoms can not be created
  nor destroyed. The atoms are only rearranged.
• All the atoms that are present in the reactants
  must also be present in the products. This means
  there must be the same number of each type of
  atoms on the reactants side and the products side
  of a chemical reaction.