Chemical
Reactions
 In chemical reactions, one or more substances
change into different substances.
example: combustion
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
(starting materials) (yields)
PRODUCTS
(ending materials)
Common State Symbols in Chemical Equations
State Symbol
(s)
(l)
(g)
(aq)
Meaning
Solid
Example
(sodium chloride) NaCl(s)
Liquid
(bromine)
Br2(l)
Gaseous
(hydrogen)
H2 (g)
Aqueous (dissolved in
water)
(aqueous sodium chloride
solution)
NaCl(aq)
 Word equation:
sodium(s) + chlorine(g)
Chemical equation:
Na(s) + Cl2(g)
Examples:
sodium
sodium chloride(s)
NaCl(s)
sodium chloride
chlorine
chemical reaction
 Word 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
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?
Practice
Write the word equations:
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.
 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?
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)
 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
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
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
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
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