Chapter 18 - Chemical Changes
I. Physical and Chemical Changes
Physical Change Chemical Change
No new substances New substances formed
Little heat (usually no) A lot of heat
Substance’s properties do not change Substance’s properties change
Helpful chemical changes:
Decomposition Growth Reproduction
Photosynthesis Cooking Metal alloys
Digestion Cleaning products Medicines
Cellular respiration Fuel combustion Making products in industry
Harmful chemical changes:
Burning: Burning releases toxic gases (e.g: sulphur dioxide) into the atmosphere, this
can cause breathing problems and acid rains which kill fish and other aquatic life.
Rusting
Decomposition
These changes are brought about by interactions between matter and different forms of
energy:
Heat (section V.)
Light (section VII.)
Electricity (section VIII.)
Mixing matter (section IX.)
Indicators of chemical changes:
Color change
Precipitate formation: a solid settled after mixing certain liquids
Gas bubbles: caused when gas released
Odor change
Energy change (Temperature and Light)
II. Chemical Reaction
Reactant A + Reactant B → Product C + Product D
Reactant (s) - (Condition) → Products (s)
III. Different Phases
Solid (s) ←→ Liquid (l) ←→ Gas (g)
Expansion and Contraction
Phase shifts are physical changes because phases are reversible and no new
substances are formed.
IV. Diatomic Elements
Hydrogen H2
Nitrogen N2
, Fluorine F2
Oxygen O2
Iodine I2
Chlorine Cl2
Bromine Br2
V. Chemical Changes Caused by Heat
Combination Two or more substances form a new substance
Iron + Sulphur → Iron Sulphur
Fe + S → FeS
Combustion Combination of a substance with oxygen with heat
In the combustion of Hydrocarbon (a combination of carbon and
hydrogen atoms), CO2 and H2O are formed
Combustion cannot take place on the moon, unless there is a supply
of oxygen
Complete Combustion Incomplete Combustion
Plenty of O2 Not enough O2
Produce CO2 Forms a soot
Forms CO
Combustion → Pollutants
Hydrocarbon + Oxygen → Carbon dioxide + Water
Oxidation A process where a substance reacts with O2
(rusting) Examples:
o Rusting - oxidation of iron in the presence of water
o Burning of magnesium in O2 - product is Magnesium oxide
(MgO)
o Respiration
o Combustion
Thermal Substance breaks down into 2 or more substances by heat.
Decomposition NO OXYGEN
VI. Cellular Respiration
Breakdown of glucose in the presence of oxygen to release energy
It is a combustion reaction (product is CO2 and H2O)
Formula:
o C6H12O6 + O2 → CO2 + H2O (reverse of photosynthesis)
ATP
o Adenosine triphosphate
o Complex organic chemical - provided energy
I. Physical and Chemical Changes
Physical Change Chemical Change
No new substances New substances formed
Little heat (usually no) A lot of heat
Substance’s properties do not change Substance’s properties change
Helpful chemical changes:
Decomposition Growth Reproduction
Photosynthesis Cooking Metal alloys
Digestion Cleaning products Medicines
Cellular respiration Fuel combustion Making products in industry
Harmful chemical changes:
Burning: Burning releases toxic gases (e.g: sulphur dioxide) into the atmosphere, this
can cause breathing problems and acid rains which kill fish and other aquatic life.
Rusting
Decomposition
These changes are brought about by interactions between matter and different forms of
energy:
Heat (section V.)
Light (section VII.)
Electricity (section VIII.)
Mixing matter (section IX.)
Indicators of chemical changes:
Color change
Precipitate formation: a solid settled after mixing certain liquids
Gas bubbles: caused when gas released
Odor change
Energy change (Temperature and Light)
II. Chemical Reaction
Reactant A + Reactant B → Product C + Product D
Reactant (s) - (Condition) → Products (s)
III. Different Phases
Solid (s) ←→ Liquid (l) ←→ Gas (g)
Expansion and Contraction
Phase shifts are physical changes because phases are reversible and no new
substances are formed.
IV. Diatomic Elements
Hydrogen H2
Nitrogen N2
, Fluorine F2
Oxygen O2
Iodine I2
Chlorine Cl2
Bromine Br2
V. Chemical Changes Caused by Heat
Combination Two or more substances form a new substance
Iron + Sulphur → Iron Sulphur
Fe + S → FeS
Combustion Combination of a substance with oxygen with heat
In the combustion of Hydrocarbon (a combination of carbon and
hydrogen atoms), CO2 and H2O are formed
Combustion cannot take place on the moon, unless there is a supply
of oxygen
Complete Combustion Incomplete Combustion
Plenty of O2 Not enough O2
Produce CO2 Forms a soot
Forms CO
Combustion → Pollutants
Hydrocarbon + Oxygen → Carbon dioxide + Water
Oxidation A process where a substance reacts with O2
(rusting) Examples:
o Rusting - oxidation of iron in the presence of water
o Burning of magnesium in O2 - product is Magnesium oxide
(MgO)
o Respiration
o Combustion
Thermal Substance breaks down into 2 or more substances by heat.
Decomposition NO OXYGEN
VI. Cellular Respiration
Breakdown of glucose in the presence of oxygen to release energy
It is a combustion reaction (product is CO2 and H2O)
Formula:
o C6H12O6 + O2 → CO2 + H2O (reverse of photosynthesis)
ATP
o Adenosine triphosphate
o Complex organic chemical - provided energy
