Balancing Equations

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Balancing Equations

• Balancing, Writing, and Naming Equations

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Balancing Equations
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Balancing Equations

• Law of Conservation of Matter
• In a chemical reaction, matter can be neither
  created nor destroyed.
• In a chemical reaction, the amount of reactants
  equal the amount of products.
• So, the mass of the reactants and products should
  equal each other if this law is followed.

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Balancing Equations

• Paraphrase
• Law of Conservation of Atoms
• The number of atoms of each type of element must
  be the same on each side of the equation.

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Balancing Equations

• Balancing hints
• Balance the metals first.
• Balance the ion groups next.
• Balance the other atoms.
• Save the non ion group oxygen and hydrogen until
  the end.

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Balancing Equations

• Hydrogen oxygen water
• H2 O2 H2O

• Hydrogen and oxygen are diatomic elements.
• Their subscripts cannot be changed.
• The subscripts on water cannot be changed.

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Balancing Equation

• H2 O2 H2O

• Count the atoms on each side.
• Reactant side 2 atoms H and 2 atoms O
• Product side 2 atoms H and 1 atom O

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Balancing Equations

• H2 O2 H2O
• If the subscripts cannot be altered, how can the
  atoms be made equal?
• Adjust the number of molecules by changing the
  coefficients.

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Balancing Equations

• H2 O2 2H2O

• Balance one atom at a time Lets start with
  balancing oxygen!
• Use the distribution rule from math class to
  balance equations!
• Ex. 3 (x 2) 3x 6
• Reactants 2 atoms of H and 2 atoms of O
• Products 4 atoms of H and 2 atoms of O
• H is no longer balanced!

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Balancing Equations

• 2H2 O2 2H2O

• Now try to balance the hydrogens by placing a 2
  in front of the reactant H2
• Reactant side 4 atoms of H and 2 atoms of O
• Product side 4 atoms of H and 2 atoms of O
• Its Balanced!

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Balancing Equations

• N2 H2 NH3
• Nitrogen hydrogen ammonia

• Count atoms.
• Reactants 2 atoms N and 2 atoms H
• Products 1 atom N and 3 atoms of NH3

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Balancing Equations

• Nothing is balanced.
• Balance the nitrogen first by placing a
  coefficient of 2 in front of the NH3.

• N2 H2 2NH3

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Balancing Equations

• Hydrogen is not balanced.
• Place a 3 in front of H2.
• Reactant side 2 atoms N, 6 atoms H
• Product side 2 atoms N, 6 atoms H
• Its balanced!

• N2 3H2 2NH3

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Balancing Equations

• Cu H2SO4
• CuSO4 H2O SO2

• Count Atoms
• Reactants Cu 1, H 2, S 1, O 4
• Products Cu 1, H 2, S - 2, O - 7

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Balancing Equations

• Sulfur is not balanced.
• Place a two in front of sulfuric acid.
• Count atoms 2 H2SO4 H 4, S 2, O - 8

• Cu 2H2SO4
• CuSO4 H2O SO2

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Balancing Equations

• Hydrogen needs to be balanced so place a 2 in
  front of the H2O.
• Count the number of atoms.

• Cu 2H2SO4
• CuSO4 2H2O SO2

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Balancing Equations

• Reactants Cu 1, H 4, S 2, O 8
• Products Cu 1, H 4, S 2, O 8
• Its balanced!

• Cu 2H2SO4
• CuSO4 2H2O SO2

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Balancing Equations

• Ca3(PO4)2 H2SO4 CaSO4 H3PO4

• Count atoms.
• Reactants Ca 3 atoms, P 2 atoms, O 8
  atoms H atoms, S 1 atom, O 4 atoms

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Balancing Equations

• Side note on Ca3(PO4)2
• The subscript after the phosphate indicates two
  phosphate groups.
• This means two PO43- groups with two P and eight
  O atoms.

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Balancing Equations

• Ca3(PO4)2 H2SO4 CaSO4 H3PO4

• Count atoms in the product.
• Ca atoms 1, S atom 1, O atoms 4 H atoms
  3, P atom 1, O atoms - 4

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Balancing Equations

• In this equation, the ion groups do not break up.
• Instead of counting individual atoms, ion groups
  may be counted.

• Ca3(PO4)2 H2SO4 CaSO4 H3PO4

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Balancing Equations

• Ca3(PO4)2 H2SO4 CaSO4 H3PO4

• Reactants Ca2 3, PO43- - 2, H 2, SO42 -
  1
• Products Ca2 - 1, SO42- - 1, H - 3, PO43- - 1

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Balancing Equations

• Balance the metal first by placing a coefficient
  of 3 in front of CaSO4.
• Products Ca 3 atoms, SO42- - 3 groups

• Ca3(PO4)2 H2SO4 3CaSO4 H3PO4

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Balancing Equations

• Three sulfate groups are needed on the reactant
  side so place a coefficient of 3 in front of
  H2SO4.
• 3H2SO4 gives 6 H and 3 SO42-.
• Neither phosphate nor calcium is balanced.

• Ca3(PO4)2 3H2SO4 3CaSO4 H3PO4

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Balancing Equations

• A coefficient of 2 placed in front of H3PO4 which
  balances both hydrogen and phosphate.

• Ca3(PO4)2 3H2SO4 3CaSO4 2H3PO4

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Balancing Equations

• This method of balancing equations is trial and
  error.
• Practice.