Fuels, alkanes and alkenes
Do now :
Why is it going to be such a problem when crude
oil runs out in approximately 50 years?
What do I need to know?
Carbon Chemistry
Carbon chemistry (“organic chemistry”) focuses on
molecules made from carbon compounds:
Carbon always forms 4 covalent bonds. Why?
C
Crude oil
Crude oil is a finite resource found in rocks.
DARK, SMELLY LIQUID - mixture of many
different carbon compounds.
Crude oil
Crude oil straight from the ground has not
much use. It has too many substances in it.
All having different boiling points - must be
separated into fractions by distillation.
Remember - distillation separates liquids with
different boiling points.
Hydrocarbons and crude oil
Crude oil is a mixture of HYDROCARBONS
(compounds made up of carbon and
hydrogen). Some examples:
H
C
C
H
H
H
Ethane
H
H
H
H
H
C
C
C
C
H
H
H
H
Butane
H
Increasing length
H
H
Shorter chain
hydrocarbons are
in greater demand
because they have
more uses and
release more
energy during
burning.
Alkanes
Alkanes are SATURATED HYDROCARBONS. What does
this mean?
SATURATED means that all of these atoms are held
together by single bonds, for example:
H
H
H
C
C
H
H
Ethane
H
H
H
H
H
H
C
C
C
C
H
H
H
H
Butane
Alkanes are very unreactive
(but they do burn well).
H
Crude oil separation in the lab
Long video. Skip between heating to him showing the fractions in the test tube
and describing them. Then lighting them at the end.
Explain the following terms
Mark your answers in coloured pen
Small molecules with
few carbon atoms in
short chains - most
useful.
Good fuels - ignite
easily, burn well with
less smoky flames
than HC made up of
larger molecules.
FLAMMABLE!
Fractional distillation
Crude oil is separated into hydrocarbons with similar boiling points
-fractions. Each hydrocarbon fraction contains molecules with
similar number of carbon atoms.
for heating and cooking
for fuel in cars
Learn
these!
You need to know
the order, names,
trends and uses
(not temps)
The gases move up
the column and
the hydrocarbons
condense when
they reach their
boiling points.
Burning hydrocarbons (propane gas)
Write the word and symbol equation for this reaction.
Hint: burning=combustion, what are the products of
combustion?
Remember: balance your equation so that the number of
each element is balanced on both sides of the equation.
Combustion is the reaction
of a substance with oxygen
to produce carbon dioxide
and water.
Burning propane gas
Write the word and symbol equation for this reaction.
Hint: burning=combustion, what are the products of
combustion?
Remember: balance your equation so that the number of
each element is balanced on both sides of the equation.
Propane + oxygen → carbon dioxide + water
C3H8(l) + 5O2(g) → 3CO2(g) + 4H2O(g)
Complete combustion
In your book state the products of complete combustion of a
hydrocarbon. Describe and we can prove these are being
formed using the apparatus below.
Incomplete combustion
What do you think it means?
What are the products?
What is the main issue with the products?
Incomplete combustion
If there is not enough oxygen: carbon monoxide is formed instead
of carbon dioxide.
Carbon monoxide is a toxic gas. It is colourless and odourless.
Red blood cells permanently bind with this gas and carry it
around in your blood instead of oxygen.
Releases carbon monoxide
Substitution reactions of alkanes with
chlorine
Halogen + alkane –(UV)-> halogenoalkane + hydrogen halide
Must be in the
presence of
ultraviolet radiation
(UV) e.g. sunlight
UV light breaks the
Cl-Cl bond in the
halogen, creating a
free radical,
allowing it to react.
Cracking
This is a THERMAL DECOMPOSITION
reaction, with clay used as a catalyst
Cracking can be used (as well as fractional distillation) to
extract petrol from crude oil.
Cracking
In the cracker long chain molecules are split
apart or ‘cracked’. An example of such a
reaction is:
Octane
hexane
Heat
pressure
catalyst
+
Used as
a fuel
C8H18 → C6H14 + C2H4
ethene
Ethene
is used
to make
plastics
Task
Draw out displayed formulae of a pair of
products formed by cracking decane
H H H H H H H H H H
H C C C C C C C C C C H
H H H H H H H H H H
Heat
pressure
H H H H H H H H
H C C C C C C C C H
H H H H H H H H
octane
decane
catalyst
+
ethene
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