Balancing Chemical Reactions

1
Balancing Chemical Reactions
2
Steps to Success in Balancing Chemical equations

1. Figure out whose a reactant and whose a product
2. Write the formulas for the reactants on the left
   side of the arrow (if more than one, separate
   them with a )
3. Write the formulas for the products on the right
   side of the arrow (if more than one, separate
   them with a )
4. List all the atoms in the products and the
   reactants
5. Use coefficients in front of formulas to make the
   numbers of atoms in the reactants and products
   equal
6. Quiz yourself
7. Check your answers

3
Example 1 Magnesium reacts with hydrochloric
acid to form magnesium chloride and hydrogen gas
1. Figure out whose a reactant and whose a product
Reactant Product Magnesium magnesium
chloride Hydrochloric acid hydrogen
2. Write the formulas for the reactants on the
left side of the arrow (if more than one,
separate them with a )
?
Mg HCl
3. Write the formulas for the products on the
right side of the arrow (if more than one,
separate them with a )
?
Mg HCl
MgCl2 H2(g)
hydrogen is diatomic
4
Example 1 (cont) Magnesium reacts with
hydrochloric acid to form magnesium chloride and
hydrogen gas

• 4. List all the atoms in the products and the
  reactants

Mg 1 H 1 Cl 1
Mg 1 H 2 Cl 2
5. Use coefficients in front of formulas to make
the numbers of atoms in the reactants and
products equal
Mg 1 H 2 1 Cl 2 1
Mg 1 H 2 Cl 2
The coefficient multiples all the atoms in the
molecule that its in front of
5
Example 2 Barium chloride reacts with sodium
phosphate to form sodium chloride and barium
phosphate
1. Figure out whose a reactant and whose a product
Reactant Product Barium chloride sodium
chloride Sodium phosphate barium phosphate
2. Write the formulas for the reactants on the
left side of the arrow (if more than one,
separate them with a )
?
BaCl2 Na3PO4
3. Write the formulas for the products on the
right side of the arrow (if more than one,
separate them with a )
6
Example 2 (cont) Barium chloride reacts with
sodium phosphate to form sodium chloride and
barium phosphate

• 4. List all the atoms in the products and the
  reactants

Ba 1 Cl 2 Na 3 P 1 O 4
Ba 3 Cl 1 Nal 1 P 2 O 8
5. Use coefficients in front of formulas to make
the numbers of atoms in the reactants and
products equal
Ba 3 1 Cl 6 2 Na 6 3 P 2 1 O 8 4
Ba 3 Cl 6 1 Na 6 1 P 2 O 8
The coefficient multiples all the atoms in the
molecule that its in front of
7
Example 3 When heated, ammonium carbonate
breaks down into gaseous ammonia, carbon dioxide
and water vapor
1. Figure out whose a reactant and whose a product
Reactant Product Ammonium carbonate ammonia
carbon dioxide water
2. Write the formulas for the reactants on the
left side of the arrow (if more than one,
separate them with a )
?
(NH4)2CO3
3. Write the formulas for the products on the
right side of the arrow (if more than one,
separate them with a )
8
Example 3 (cont) When heated, ammonium
carbonate breaks down into gaseous ammonia,
carbon dioxide and water vapor

• 4. List all the atoms in the products and the
  reactants

N 2 H 8 C 1 O 3
N 1 H 5 C 1 O 3
5. Use coefficients in front of formulas to make
the numbers of atoms in the reactants and
products equal
N 2 H 8 C 1 O 3
N 2 1 H 8 5 C 1 O 3
The coefficient multiples all the atoms in the
molecule that its in front of
9
Example 4 In plants, carbon dioxide and water
combine to form glucose and oxygen
1. Figure out whose a reactant and whose a product
Reactant Product Carbon dioxide glucose water
oxygen
2. Write the formulas for the reactants on the
left side of the arrow (if more than one,
separate them with a )
CO2(g) H2O
?
3. Write the formulas for the products on the
right side of the arrow (if more than one,
separate them with a )
10
Example 4 (cont) In plants, carbon dioxide and
water combine to form glucose and oxygen

• 4. List all the atoms in the products and the
  reactants

C 1 H 2 O 3
C 6 H 12 O 8
5. Use coefficients in front of formulas to make
the numbers of atoms in the reactants and
products equal
C 6 1 H 12 2 O 18 3
C 6 H 12 O 16 8
The coefficient multiples all the atoms in the
molecule that its in front of
11
Your turn

• Balance the following equations
• Zinc and lead (II) nitrate react to form zinc
  (II) nitrate and lead.
• Aluminum bromide and chlorine gas react to form
  aluminum chloride and bromine gas
• A solution of silver (I) nitrate reacts with
  solid copper to form copper (II) nitrate and
  solid silver.
• Calcium hydroxide and phosphoric acid react to
  form calcium phosphate and water.
• Potassium metal reacts with chlorine gas to form
  potassium chloride.
• Iron (III) oxide reacts with hydrogen gas to form
  solid iron and water.

12
the Answers

• Zinc and lead (II) nitrate react to form zinc
  nitrate and lead.
• Zn Pb(NO3)2 ? Zn(NO3)2 Pb
  already balanced
• Aluminum bromide and chlorine gas react to form
  aluminum chloride and bromine gas
• 2 AlBr3 3 Cl2 (g) ? 2 AlCl3 3 Br2
  (g)
• A solution of silver (I) nitrate reacts with
  solid copper to form copper (II) nitrate and
  solid silver.
• 2 Ag(NO3) Cu ? Cu(NO3)2 2Ag
• Calcium hydroxide and phosphoric acid react to
  form calcium phosphate and water.
• 3 Ca(OH)2 2 H3PO4 ? Ca3 (PO4)2 6 H2O
• Potassium metal reacts with chlorine gas to form
  potassium chloride.
• 2 K Cl2 (g) ? 2 KCl
• Iron (III) oxide reacts with hydrogen gas to form
  solid iron and water.
• Fe2O3 3 H2 (g) ? 2 Fe 3 H2O