Chemistry C1 5.1 Cracking hydrocarbons.

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How can hydrocarbon molecules be broken down?
By heating them with steam to a very high temperature of by passing their vapours over a hot catalyst.
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What does cracking produce?
Alkanes and alkenes.
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What are alkenes?
Unsaturated hydrocarbons.
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What colour do alkenes turn bromine water?
From orange to colourless.
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What is the process called when large hydrocarbon molecules are broken down into smaller molecules?
Cracking.
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What two ways can cracking be done?
1) By heating a mixture of hydrocarbon vapours and steam to a very high temperature. 2) By passing hydrocarbon vapours over a hot catalyst.
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What happens during cracking?
Thermal decomposition reactions produce a mixture of smaller molecules.
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What molecules are produced through cracking?
Smaller molecules, some of which are alkanes - which are saturated hydrocarbons, and some of which are alkenes - unsaturated hydrocarbons.
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What are alkanes more useful than alkenes as?
Fuels.
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What is the general formula of an alkane?
C_(n)H_(2n+2).
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What s the general formula of alkenes?
C_(n)H_(2n).
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How are alkenes unsaturated hydrocarbons?
Because they contain fewer hydrogen atoms than alkanes with the same number of carbon atoms.
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What makes alkenes more reactive than alkanes?
They have a double bond between two carbon atoms.
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How can different mixtures of alkanes and alkenes be produced by cracking?
Because different hydrocarbons can be used and the conditions for the reaction can be changed.
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What reason might an oil company want to crack large hydrocarbons to make smaller alkanes?
To make fuels that are more useful or for which there is more demand, large hydrocarbons do not burn easily and are less in demand.
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How are alkenes different from alkanes?
Alkenes are unsaturated, have a double bond, have a different general formula, have fewer hydrogen atoms than the corresponding alkane, are more reactive, react with or decolourise bromine water.
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**LOOK UP AN EXAMPLE OF A CRACKING REACTION**
*LOOK UP MOLECULES OF ALKENE DIAGRAMS ETC**
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Card 2

Front

What does cracking produce?

Back

Alkanes and alkenes.

Card 3

Front

What are alkenes?

Back

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Card 4

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What colour do alkenes turn bromine water?

Back

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Card 5

Front

What is the process called when large hydrocarbon molecules are broken down into smaller molecules?

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