1. 5.1 PHYSICAL AND CHEMICAL CHANGES.
Two types of changes involved in matter:
*Physical changes
*Chemical changes
a) Physical Changes
1. Physical change are defined as the changes that only affect the physical properties of substances.
2. The characteristics of physical change are:
 Involves only physical changes such as shape or size of a substance.
 Involves changes in the state of matter; solid, liquid and gas.
 Chemicals composition and chemical properties of substances remain unchanged so that no new
substances are formed.
 Less energy is needed.
 The changes are reversible.
3. Physical changes in our daily life are:
(a) *Melting of ice:
(b) Freezing:
(c) *Evaporation of water:
(d) Natural water cycle.

2. (e) Condensation:
(f) Dissolving salt and sugar in water.
(g) Formation of dew on the grass.
4. Physical changes being studied in a laboratory are:
(a) Sublimation:
b) Chemical Changes
1. Defined as the changes that affect the chemical composition and chemical properties of the substances.
2. The characteristics of chemical change are:
 New substances known as products.
 Chemical composition and chemical properties of the new substances are different from the original
substance which is known as reactant.
 Is usually fixed and irreversible.
 Needs large amount of energy.
3. Chemical changes in our daily life are:
 Respiration.
 Burning of paper or fossil fuels produces carbon dioxide and ash.
 Digestion of food.
 Washing dishes with detergent or washing hair using shampoo.
 Change in colour of peeled apple when exposed to air.
 Decomposition of animal carcasses.
 Making bread from wheat flour.
 Photosynthesis.

3. 4. Examples of chemical changes being studied in a laboratory are:
(a) Respiration
Oxygen + glucose --------> carbon dioxide + water vapour + energy
(b) Neutralisation:
Acid + alkali + -------> salt = water
(c) Electrolysis of water.
COMPARING AND CONTRASTING PHYSICAL AND CHEMICAL CHANGES
5.2 HEAT CHANGE IN CHEMICAL REACTIONS
a) Chemical Reaction Involves Heat Change
1. Chemical reactions involves changes in energy in the form of heat energy.
2. Chemical reactions:-
 energy is aborded to break bonds in the reactants.
 energy is released when new bonds sre formed in the products.
3. Chemical reaction that absorbs energy is dissolving ammonium chloride in water. When ammonium
chloride (Salt) is put into a beaker of water which is held with our hands, we can feel that the temperature
of water falls. This is because the reaction in the beaker absorbs energy from the water and our hands.
4. Chemical reactions that releases energy is dissolving sodiumhydroxide in water. When sodium hydroxide
(SOAP) is put into a pail of water and stirred using our hands, we can feel that the soap solution becomes
hot. This is because the reaction releases heat into the surroundings.
b) Reaction Involving Heat Loss And Heat Gain.
Chemical reactions can be classified into two groups:
 Exothermic reactions.
 Endothermic reactions

4. Exothermic reactions
1. Exothermic reactions is defined as a reaction which releases energy in the form of heat into the
surrounding (heat loss), and causes the surrounding temperature to increase.
2. The characteristics of exothermic reactions are:
 Heat is released into the surroundings.
 Energy is released when bonds are formed because the energy needed to break the bond in the
reactants is less than the energy released when new bonds are formed in the products.
 Surrounding temperature increases due to the release of energy but the temperature of mixture
decreases.
 Energy content of the reactant(s)
 Higher energy content of the product(s)
Endothermic reactions
1. Absorb energy or gain heat (surrounding temperature to decrease).
2. The characteristics of exothermic reaction are:
 Heat is absorbed.
 Energy is aborded.
 Surrounding temperature decreases and temperature of the mixture increases.
 Energy content of the reactant(s) is lower than energy content of the product(s)
3. Endothermic reactions are:
 Boiling water.
 Heating copper sulphate crystals.
 Melting wax.
 Dissolving ammonium chloride in water.
 Photosynthesis.
 Decomposition of mercury oxide by heat and decomposition of copper carbonate by heat.
c)Heat Changes In Industrial Chemical Reactions
 Haber Process
 Contact Process
Haber Process
1. The production of ammonia through the Haber process involves the reaction between nitrogen and
hydrogen gases mixed in the proportional 1:3
2. The Haber process is an exothermic reaction. It is a reversible reaction (forward and backward reaction).
3. Catalyst (iron) at a temperature of 450-500°C and a pressure of 200-250 atmospheres.

5. The Haber Process
Contact Process
1. The Contact process is an industrial process to produce sulphuric acid
2. Catalyst (vanadium(V) oxide) at a temperature of 450-500°C and a pressure 1 atm.
3. Sulphurid acid is used:-
 In the production of chemical fertilisers
 In the production of detergent
 As the electrolyte in accumulators (batteries)
 As a dehydrating agent
The Contact Process
5.3 THE REACTIVITY OF METALS.
 Reactions of metal with water
 Reactions of metal with acid
 Reactions of metal with oxygen

6. Reactions of metal with water.
1. The most reactive metals can react with cold water to produce alkaline solutions and hydrogen.
2. There are only three metals that can react with water: potassium, sodium and calcium
Reactions of metal with acid
1. Most metals (i.e. metals that are placed above hydrogen in the electrochemical series) can react with acids
2. During the reaction, the metal displaces hydrogen from the acid to form a salt and hydrogen gas
3. Metal + acid = salt + hydrogen
Reactions of metal with oxygen.
1. Metal + oxygen = metal oxide
2. The reactivity of metals with oxygen decreases down the reactivity series of metals.
3. The metal oxide produced a different colour compared to the original metal.

7. COMPARING AND CONTRASTING THE REACTIVITY OF METALS WITH WATER, ACIDS AND OXYGEN.
The Reactivity Series Of Metals.
The reactivity series order of reactivity with oxygen

8. The Position Of Carbon In The Reactivity Series Of Metals.
1. The reactivity series of metals shows the inclination of a metal to react with oxygen.
2. The operational definition of this experiment is carbon reduces a metal oxide to its metal if carbon is more
reactive than the metal.
Metal oxide X + carbon = carbon dioxide + metal X
3. On the other hand, carbon does not react with a metal oxide if it is less reactive than the metal.
5.4 APPLICATION OF THE REACTIVITY SERIES OF METALS
a) Method of Extraction of Metals
 Depend on their positions in the reactivity series.
 Metals placed below carbon in the reactivity series can be extracted from their ores by heating their
ores with carbon
 Electrolysis is only used to extract metals from their ores if the metals are more reactive than carbon

9. b) The importance of the reactivity series are:
 Determine the method of extracting the metal.
 Predict the reactivity of a particular metal.
 Predict whether a particular metal can remove oxygen from another metal oxide.
5.5 ELECTROLYSIS
1. Electrolysis is the decomposition of electrolytes by electric current
2. During electrolysis, electrical energy changes to chemical energy
Term Explanation
Electrolyte a substances (in liquid or molten state) that allows electricity to flow through it.
Electrode carbon rod or platinum sheet dipped in the electrolyte
Anode positive electrode connected to the positive source of the battery
Cathode negative electrode connected to the negative source of the battery
Anions negative ions that are attracted to the anode
Cations positive ions that are attracted to the cathode
3. The process that occurs during electrolysis
 Cations are attracted to the cathode. At the cathode, cations receive electrons and are discharged to
form neutral atoms.
 Anions are attracted to the anode. At the anode, anions release electrons and are discharged to form
neutral atoms.
Electrolysis In Industry
 Extraction of metals
 Purification of metals
 Electroplating of metals

10. Extraction of metals
1. Metals placed above carbon in the reactivity series of metals can be extracted from their oxides by
electrolysis
2. Examples:
 Extraction of aluminium from aluminium oxide (bauxite)
 Extraction of sodium from sodium chloride
Purification of metals
1. The following conditions must be satisfied:
 Anode: the strip of impure metal
 Cathode: the strip of pure metal
 Electrolyte: a salt solution containing the ions of the metal that is to be purified.
2. Example: purification of copper metal
 Anode: the impure copper
 Cathode: the pure copper
 Electrolyte: copper sulphate solution
Electroplating of metals
1. Electroplating is defined as the process of covering the surface of a metal with another metal with
electrolysis.
2. The reasons for electroplating are:
 To prevent and protect metals from corrosion and rusting
 To make a metal surface look more attractive
3. In electroplating, the following conditions must be satisfied
 Anode: the plating metal
 Cathode: the object that is to be electroplated
 Electrolysis: a salt solution containing the plating metal
4. Example: electroplating an iron spoon with silver
 Anode: silver metal
 Cathode: iron spoon
 Electrolysis: silver nitrate solution
5.6 THE PRODUCTION OF ELECTRICAL ENERGY FROM CHEMICALS REACTIONS
Simple cells
1. A simple cells consists of two metal electrodes which are different in reactivity and immersed in an
electrolyte
2. The polarity of the cell depends on the positions of the two metals in the reactivity series

11. 3. Various types of cells
Type of cell Users Advantages Disadvantages
Dry cell used in radios,
torches, toys, electric
shavers, cameras,
alarm clock
 Light and can be found
in variety of sizes
 Electrolytes cannot spill
 The current produced
is firm because
polarization is
overcome
 Cannot last long
 The electric current
that is produced is
small
 Cannot be recharged
when it is fully
discharged
Lead-acid
accumulator
used to supply energy
to cars, lorries, and
hospital emergency
equipment
 It can be recharged
when fully discharged
 The current and
voltage produced are
large and constant
 Long lasting
 It is heavy and difficult
to carry
 It can be easily spoilt
and can lose its charge
if it is not used for a
long time
 Its electrolyte cell spill
easily
Alkaline
battery
used to supply a large
amount of electrical
energy, useful for
clocks and games
equipment
 Long lasting
 The current and
voltage produced are
large and constant
non rechargeable
silver oxide-
mercury
battery
used in watches,
calculators and
hearing aids
 It is small in size and
easy to carry
 The current and
voltage produced are
large and constant
 Long lasting
 It is expensive
 non rechargeable
nickel
cadmium
battery
used in electronic
devices
 It can be recharged
 Long lasting
it is expensive

12. 5.7 CHEMICAL REACTIONS THAT OCCUR IN THE PRESENCE OF LIGHT.
a) Photosynthesis
1. In photosynthesis, sunlight is absorbed by the chlorophyll in the leaves and a biochemical reaction is
carried out
Carbondioxide +water --------------------------- > glucose + oxygen
2. Importance: to maintain the percentage of composition of oxygen and carbon dioxide in the atmosphere
and to provide food to plants.
b) Effect of Light on a Photosensitive Chemicals
1. Photographic films are made of plastic strips covered with an emulsion consisting of gelatin and silver
bromide crystals
2. To snap a picture, the filmmust exposed to light
3. The part of the filmthat is exposed to light will undergo chemical reaction
4. The exposed filmis then processed by using sodium thiosulphate solution to remove the unexposed layer
5. The product is a negative image on the photographic film.
6. Storing:
 Film must be wrapped in black plastic wrapper or put in a black box to prevent it from exposed to light
 Some medicine must be stored in dark bottles to prevent them from being spoilt
7. Examples of photosensitive chemicals:
 Silver salt
 Hydrogen peroxide
 Chlorine water
 Sodium hypochlorite
5.8 USE OF CHEMICAL REACTIONS AS SOURCES OF ENERGY
1. Chemical reactions enable us to extract active metals from their ores using electrolysis
2. Electroplating can produce attractive product that can resist corrosion and rusting
3. The changes of chemical energy to electrical energy enables us to build various types of chemical cells for
supply of power