What you will need to remember from year 10

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C1b4.1 Cracking
Hydrocarbons Key Points We can split large
hydrocarbon molecules up into smaller
molecules by heating them and passing the gas
over a catalyst. Cracking produces unsaturated
hydrocarbons, which we call alkenes. Alkenes
burn, and also react with bromine
water, producing colourless products.
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Hydrocarbons and crude oil
Crude oil is a mixture of HYDROCARBONS (compounds
made up of carbon and hydrogen). Some examples

• Longer chains mean
• Less ability to flow
• Less flammable
• Less volatile
• Higher boiling point

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Cracking
Shorter chain hydrocarbons are in greater demand
because they burn easier as fuels. They can be
made from long chain hydrocarbons by cracking
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Alkanes
Alkanes are SATURATED HYDROCARBONS. What does
this mean? HYDROCARBONS are molecules that are
made up of hydrogen and carbon atoms SATURATED
means that all of these atoms are held together
by single bonds, and each molecule contains as
much hydrogen as possible for example
Alkanes are fairly unreactive (but they do burn
well).
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Alkenes
Alkenes are different to alkanes they contain
DOUBLE COVALENT bonds. For example
ALKENES
ALKANES
This double bond means that alkenes have the
potential to join with other molecules this
make them REACTIVE. We can test for alkenes
because they turn bromine water colourless.
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C1b4.1 Cracking hydrocarbons
List the similarities and differences of these
hydrocarbons
C - H bond
H
C
Differences
Similarities
Same number of Carbon atoms
Different numbers of hydrogen atoms
Hydrogen atoms all have one bond
Butane is saturated, Butene is unsaturated
Carbon atoms all have 4 bonds
Butane has C-C, Butene has C C
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Recall - heating calcium carbonate
Cracking is an example of Thermal decomposition
(Remember -heating calcium carbonate) The
breaking down of a substance into smaller
simpler substances by the action of heat
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Cracking
This is a THERMAL DECOMPOSITION reaction, with
clay used as a catalyst
Cracking is an example of Thermal decomposition
(Remember -heating calcium carbonate) The
breaking down of a substance into smaller
simpler substances by the action of heat
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Test for a saturated or unsaturated hydrocarbon
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