IGCSE
chemistry
section 3
Reactions
of alkanes and alkenes
Alkanes
As
alkanes are saturated they are not reactive.
However, there are three types of reactions they carry out.
1.
Combustion
This
is our luck as we use the shorter alkanes as fuels. Combustion is an exothermic
reaction. During complete combustion
(which means in enough oxygen) alkanes produce carbon dioxide and water. When there is not sufficient oxygen carbon
monoxide or carbon and water are produced.
a. Write a word equation for the complete
combustion of methane.
b. Write a balanced symbol equation for
the complete combustion of methane.
c. Write a word equation for the
incomplete combustion of ethane to form carbon monoxide and water.
2.
Substitution
The
balanced symbol equation below shows another type of reaction of alkanes. This
reaction only happens in the presence of UV light (i.e. sunlight).
CH4 +
Br2 ® CH3Br + HBr
a. Make the reactants with the ball and
sticks – use green for bromine and “do” the reaction.
b. Describe what has happened during the
reaction.
c. Rewrite the equation using displayed
formula.
3. Cracking
The
longer alkanes are not so good as fuels because they do not burn easily so they
are used to make alkenes by a reaction called cracking. More on this reaction in section 5c.
Alkenes
1.
Combustion
a. Write a word equation for the complete
combustion of ethene.
b. Write a balanced symbol equation for
the complete combustion of ethene.
We
don’t use alkenes as fuels because they are more useful to us because of the
reaction below.
2.
Addition
The
balanced symbol equation below shows another type of reaction of alkenes. This
reaction happens in any condition even in the dark!!
C2H4 +
Br2 ® C2H4Br2
a. Make the reactants with the ball and
sticks – use green for bromine and “do” the reaction.
b. Describe what has happened during the
reaction.
c. Rewrite the equation using displayed
formula.
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