Balancing Equations

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Balancing Equations

• CHEM

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Chemical equations tell you the following

• The substances that react together.
• The substances that are formed.
• The amounts of each substance involved.
• The arrow ? is read as "yields".
• Most chemical reactions are written with the
  arrow pointing from left to right like this ?
  from reactant to product

HCl NaOH ? NaCl H2O
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Balanced Equations

• The equation below is "balanced".
• S8 12O2 ? 8SO3
• Balanced equations have the same number of each
  type of atom on both sides of the arrow.
• Why?

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These numbers are found in a chemical equation

• Subscripts
• Coefficients
• The balanced equation S8 12O2 ? 8SO3 tells us
  that one molecule of S8 reacts with twelve
  molecules of O2 to produce eight molecules of
  SO3.

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Using coefficients and subscripts to count atoms
in equations

• number of atoms coefficient X subscript

• Example
• 2H2O
• of H atoms coefficient 2 X subscript 2 4
• of O atoms coefficient 2 X subscript 1 2
• of atoms coefficient X subscript inside ( ) X
  subscript outside ( )
• 2Al2(SO4)3
• of Al atoms 2 X 2 4
• of S atoms 2 X 1 X 3 6
• of O atoms 2 X 4 X 3 24

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Balancing Steps

• 1. Write the unbalanced equation.
• 2. Count atoms on each side.
• 3. Add coefficients to make s equal.
• Coefficient ? subscript of atoms
• 4. Reduce coefficients to lowest possible
  ratio, if necessary.
• 5. Double check atom balance!!!

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Helpful Tips

• Balance one element at a time.
• Update ALL atom counts after adding a
  coefficient.
• If an element appears more than once per side,
  balance it last.
• Balance polyatomic ions as single units.
• 1 SO4 instead of 1 S and 4 O
• Check for Diatomic molecules
• H2 - N2 - O2 - F2 - Cl2 - Br2 - I2
• Balance in the following order
• Metals ? Nonmetals ? Oxygen ? Hydrogen

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Balance the equations listed below

• NaOH ?Na2O H2O
• Fe O2 ?Fe2O3
• CO2 H2O ?C6H12O6 O2
• FeS HCl ?FeCl2 H2S
• O2 H2 ?H2O
• Cl2 NaI ?NaCl I2
• Al(NO3)3 H2SO4 ?Al2(SO4)3 HNO3

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Check your Answers

• 2 NaOH ?Na2O H2O
• 4 Fe 3O2 ?2 Fe2O3
• 6 CO2 6 H2O ?C6H12O6 6 O2
• FeS 2 HCl ?FeCl2 H2S
• O2 2 H2 ?2 H2O
• Cl2 2 NaI ?2 NaCl I2
• 2 Al(NO3)3 3 H2SO4 ?Al2(SO4)3 6 HNO3