1. Chemical Reactions

2. In chemical reactions, one or more substances
change into different substances.
example: combustion

3. Word Equations and Chemical Equations
Chemists use equations to describe chemical reactions.
Word equations show the names of the materials in the chemical reaction.
Chemical equations show the chemical formulas of the materials in the chemical reaction.
REACTANT
PRODUCTS
(starting materials) (yields) (ending materials)

4. Common State Symbols in Chemical Equations
Meaning
Example
Solid
Liquid
Gaseous
Aqueous (dissolved in water)
(s)
(sodium chloride) NaCl(s)
(l)
(bromine) Br2(l)
(g)
(hydrogen) H2 (g)
(aq)
(aqueous sodium chloride solution) NaCl(aq)

5. sodium(s) + chlorine(g) sodium chloride(s)
Word equation:
sodium(s) + chlorine(g) sodium chloride(s)
Chemical equation:
Na(s) + Cl2(g) NaCl(s)
Examples:
sodium
sodium chloride
chlorine
chemical reaction

6. Word equation: Chemical equation: zinc copper(II) sulphate
zinc sulphate + copper + energy
Chemical equation:
Zn(s) + CuSO4(aq)
ZnSO4(aq) + Cu(s) + energy
zinc
copper(II) sulphate
zinc sulphate
copper

7. Consider the following reaction:
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
1. Name the reactants and products in this reaction.
2. Name the chemicals that are dissolved in water.
3. Name the white solid.
4 What physical properties do both reactants have in common?

8. Practice Write the word equations:

9. The Law of Conservation of Mass
Chemist Antoine Lavoisier’s work in the 1700s resulted in the Law of Conservation of Mass. It states that:
In a chemical reaction, the total mass of the products is always the same as the total mass of the reactants.

10. For example: The electrolysis of water
H2O  H2 + O2 is NOT a balanced chemical equation.
Why? Because the number of H and O atoms in the reactants does not equal the number of H and O atoms in the products.
How can we make a balanced chemical equation?

11. Balancing Chemical Equations
The electrolysis of water yields oxygen gas and hydrogen gas.
a) Write the word equation.
water  oxygen + hydrogen
b) Write the skeleton equation.
H2O(l)  O2(g) + H2(g)
c) Write the balanced chemical equation.
2H2O(l)  O2(g) + 2H2(g)

12. Iron reacts with oxygen to produce Iron (III) oxide (Fe2O3)
a) Write the word equation.
iron + oxygen  iron (III) oxide
b) Write the skeleton equation.
Fe + O2  Fe2O3
c) Write the balanced chemical equation.
4Fe + 3O2  2Fe2O3

13. Practice For the following reactions, write: the word equation
the skeleton equation (unbalanced chemical equation)
the balanced equation
1. Potassium hydroxide and hydrogen are produced when potassium is placed in water.
2K + 2H2O  2KOH + H2
2. The iron reacts with oxygen to produce rust, which is iron (III) oxide.
4Fe + 3O2  2Fe2O3

14. 3. Zinc reacts with lead (IV) nitrate to produce zinc nitrate and lead
3. Zinc reacts with lead (IV) nitrate to produce zinc nitrate and lead. 2Zn + Pb(NO3)4  2Zn(NO3)2 + Pb 4. Calcium chloride reacts with silver nitrate to produce a white precipitate, silver chloride, and calcium nitrate. CaCl2 + 2AgNO3  2AgCl + Ca(NO3)2 5. Calcium carbonate decomposes into calcium oxide and carbon dioxide. CaCO3  CaO + CO2

15. 6. Carbon monoxide and hydrogen gases are produced when carbon is placed in water.
C + H2O  CO + H2
7. In a hydrogen bomb, hydrogen gas and oxygen reacted to make water.
2H2 + O2  2H2O
8. Nitrogen monoxide from automobile exhaust reacts with oxygen to produce nitrogen dioxide, which is a toxic brown gas.
2NO + O2  2NO2

16. 9. Hydrogen sulphide can be broken into hydrogen gas and sulphur
9. Hydrogen sulphide can be broken into hydrogen gas and sulphur. H2S  H2 + S 10. Calcium metal and water combine to produce calcium hydroxide and hydrogen gas. Ca + 2H2O  Ca(OH)2 + H2