1. Balancing Chemical Reactions

2. Steps to Success in Balancing Chemical equations
Figure out whose a reactant and whose a product
Write the formulas for the reactants on the left side of the arrow (if more than one, separate them with a “+”)
Write the formulas for the products on the right side of the arrow (if more than one, separate them with a “+”)
List all the atoms in the products and the reactants
Use coefficients in front of formulas to make the numbers of atoms in the reactants and products equal
Quiz yourself
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 + HCl
MgCl2 + H2(g)* 
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 + 2 HCl
MgCl2 + H2(g)* 
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 “+”)
NaCl + Ba3(PO4)2 
BaCl2 + Na3PO4

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
NaCl + Ba3(PO4)2 
BaCl2 + Na3PO4
Ba 1
Cl 2
Na 3
P 1
O 4
Ba 3
Cl 1
Na 1
P 2
O 8
5. Use coefficients* in front of formulas to make the numbers of atoms in the
reactants and products equal
6 NaCl + Ba3(PO4)2 
3 BaCl Na3PO4
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 “+”)
(NH4)2CO3 
NH3(g) + CO2(g) + H2O(g)

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
(NH4)2CO3 
NH3(g) CO2(g) + H2O(g)
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
(NH4)2CO3 
2 NH3(g) CO2(g) + H2O(g)
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 “+”)
CO2(g) H2O 
C6H12O6 + O2(g)

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
CO2(g) H2O 
C6H12O O2(g)
C 1
H 2
O 3
C 6 H
O 8
5. Use coefficients* in front of formulas to make the numbers of atoms in the
reactants and products equal
6 CO2(g) H2O 
C6H12O O2(g)
C 6 1
H 12 2
O 18 3
C 6 H
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) Pb already balanced
Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas
2 AlBr Cl2 (g)  2 AlCl 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) Ag
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.
Fe2O H2 (g)  2 Fe H2O