The document discusses chemical equations and balancing chemical reactions. It explains that chemical equations are used to represent chemical reactions and must be balanced so that the same number of atoms are on both sides of the reaction arrow. It provides examples of balancing various chemical equations by adding coefficients in front of chemical formulas like 2Na + Cl2 → 2NaCl. It also notes that state symbols should be included to indicate if reactants and products are solids, liquids, gases or aqueous.

1. Mg
Mg
O2 MgO
MgO

2. Example: Formation of Lead bromide
During chemical change:
– A new compound (with different properties
from the reactants) is formed
– Energy is absorbed or given off
– Very difficult to reverse
Lead (II) Bromide
Lead Bromine
Energy

3. A chemical reaction involves the combination of two or more
reactants to give products
Lead (II) Bromide
Lead Bromine
Chemical change is usually observed during a chemical reaction

4. Chemical reactions are usually represented by
equations
EXAMPLE Reactants Products
Word Equation Magnesium + Oxygen  Magnesium oxide
Chemical equation 2Mg(s) + O2(g)  2MgO(s)
Equations can be of two types:
• Word equations
• Chemical equations

5. Chemical equations are a short form of word
equations
They consist of the:
– Chemical formulas of the reactants
– Chemical formulas of the products
separated by an arrow.
Mg + S  MgS
Pb + Br2  PbBr2

6. • Iron + Sulphur  Iron (II) sulphide
• Magnesium oxide + water  Magnesium hydroxide
• Hydrochloric acid + Sodium hydroxide  Sodium
chloride + Water
• Ammonia + Water  Ammonium hydroxide

7. There are some substances which when put in
equations, must be written with a small 2 next
to them. These are:
- Hydrogen: H2
- Oxygen: O2
- Nitrogen: N2
- Group 7: F2, Cl2, Br2, I2
This is because in nature they exist

8. • Magnesium + bromine  Magnesium bromide
• Calcium + fluorine  Calcium fluoride
• Hydrogen + Sulphur  Hydrogen sulphide
• Magnesium + water (steam)  Magnesium oxide + hydrogen

9. Mg
Mg
O2 MgO
MgO

10. sodium + chlorine  sodium chloride
Na + Cl2  NaCl
Does the equation seem right to you?
The above equation is not good enough!!
It is UNBALANCED
Na
Na
Cl
Cl
Cl
2 atoms of chlorine
1 atom of sodium
1 ion of chlorine
1 ion of sodium

11. For an equation to be balanced the number of atoms
on the right hand side must be equivalent to the
number of atoms of the right hand side
Na
Na
Cl
Cl
Cl
2 atoms of chlorine
2 atom of sodium
2 ion of chlorine
2 ions of sodium
Na
Na Cl
Equations are balanced by adding numbers in front of
the chemical symbols
2Na + Cl2  2NaCl

12. Try These!!!!
• Na + O2 → Na2O
• H2 + O2  H2O
• Al + Br2  AlBr3
• H2SO4 + NaOH  Na2SO4 + H2O
• sdNaOH + Pb(NO3)2  Pb(OH)2 + NaNO3
• Al(OH)3 + HBr → AlBr3 + H2O

14. Try these
• Calcium carbonate + hydrochloric acid  calcium chloride + water + carbon dioxide
• Hydrochloric acid + zinc  zinc chloride + hydrogen
• Iron + oxygen  Iron (III) oxide
• Potassium + bromine  potassium bromide
• Potassium hydroxide + sulfuric acid  potassium sulfate + water
• Lithium + water  lithium hydroxide + hydrogen

15. • State symbols should be included in the
equation.
• The state symbols are:
(s) = Solid
(l) = liquid
(g) = gas
(aq) = aqueous (dissolved in solution)
E.g. Na(s) + Cl2(g)  2NaCl(s)

16. • Solids
– All metals except Hg (mercury)
– Some non-metals: S, C, P, I2, B
• Liquids
– Water, ethanol (C2H5OH), Br2, Hg
• Gases
– Hydrogen, oxygen, nitrogen, carbon dioxide, carbon monoxide,
helium, chlorine, fluorine
• Aqueous
– Generally all ionic compounds are aqueous (including metal + radical)
–All acids e.g. HCl, HNO3, H2SO4, H3PO4, H2CO3, CH3COOH

17. Sodium + water  Sodium hydroxide + Hydrogen
Hydrochloric acid + iron (II) carbonate  Iron (II) chloride + carbon
dioxide + water
Magnesium + Oxygen  Magnesium oxide
Sulfuric acid + copper (II) oxide  Copper (II) sulfate + water