Balancing Equations

1
Balancing Equations

• To be able to balance equations

2
Symbols

• Remember, each element has its own symbol(s) -
  all found in the periodic table
• Every symbol begins with a capital, and may have
  one or more other non-capital letters which
  follow
• E.g.
• Oxygen O
• Nitrogen N
• Sodium Na
• Magnesium Mg
• Copper Cu

3
Balancing

• A chemical reaction can be described by the
  process
• reactants ? products
• E.g. magnesium reacts with oxygen, producing
  magnesium oxide
• magnesium oxygen ? magnesium oxide
• 2Mg O2 ? 2MgO

4
Balancing

• It is key you know how to balance the equations!
• Remember there must always be the same number of
  atoms on both sides
• Numbers can only be put in front of the formula
  when it is needed

5
Magnesium Oxide

• Look at the following reaction
• magnesium oxygen ? magnesium oxide
• 2Mg O2 ? MgO
• Youll notice, that there are more green and blue
  circles on the left hand side, than there are on
  the right
• To balance this, we can add a number in front of
  the right hand side
• 2Mg O2 ? 2MgO

6
Water

• Look at the following reaction
• hydrogen oxygen ? water
• H2 O2 ? H2O
• Again there is a problem this time we have an
  oxygen atom missing from the right hand side
• To balance this, we can add a number in front of
  the right hand side
• H2 O2 ? 2H2O

7
Water

• But this is still unbalanced!
• hydrogen oxygen ? water
• H2 O2 ? 2H2O
• Finally, we can add a number in front of the
  hydrogen on the left hand side, to balance this
  up
• 2H2 O2 ? 2H2O

8
Example

• Look at the following reaction
• H2SO4 NaOH ? Na2SO4 H2O
• The formulas are correct, but the number of atoms
  on the left are different from those on the right
• Remember we can only put numbers in front of the
  symbols

9
Balancing

• H2SO4 NaOH ? Na2SO4 H20
• In the equation, there are more H atoms on the
  left, than there are on the right
• So we can add a 2 in front of the H2O on the
  right side
• H2SO4 NaOH ? Na2SO4 2H20
• Now we have too many H and O atoms on the right
  hand side, so we can put a 2 in front of the NaOH
  on the left side
• H2SO4 2NaOH ? Na2SO4 2H20
• Now everything balances!
• Left hand side 4 x H 1 x S 6 x O 2 x Na
• Right hand side 4 x H 1 x S 6 x O 2 x Na

10
Questions

• Write a word equation for what happens when
  copper burns
• How many reactants are there in this reaction?
• What are these reactants?
• What is the product of the reaction?
• When you find the mass at the end of the
  experiment, what chemical are you finding the
  mass of?
• Answers
• copper oxygen ? copper oxide
• 2 Reactants
• Reactants copper oxygen
• Product copper oxide
• You are calculating the mass of the copper oxide

11
Balance The Equations

• H2 O2 ? H2O
• H2 N2 ? NH3
• C3H8 O2 ? CO2 H2O
• Al CuO ? Al2O3 Cu
• K2O H2O ? KOH
• CaCl2 AgNO3 ? AgCl Ca(NO3)2

12
Balance The Equations

• 2H2 O2 ? 2H2O
• 3H2 N2 ? 2NH3
• C3H8 5O2 ? 3CO2 4H2O
• 2Al 3CuO ? Al2O3 3Cu
• K2O H2O ? 2KOH
• CaCl2 2AgNO3 ? 2AgCl Ca(NO3)2