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| Question | Answer |
|---|---|
| What element do all organic compounds have in common? | carbon |
| What is an alkene? | a hydrocarbon with at least one carbon-carbon double bond |
| What is the C=C grouping called? | a functional group |
| What is a group of compounds that share a functional group called? | a homologous series |
| How do successive members of a homologous series differ? | by one carbon and two hydrogens |
| Name the first four alkenes. |
• ethene C2H4 • propene C3H6 • butene C4H8 • pentene C5H10 |
| Write the general formula for alkenes. | CnH2n |
| Describe the test for alkenes. | alkenes decolourise orange bromine water
|
| Why do alkenes decolourise bromine water? | the carbon-carbon double bonds react with the bromine |
| What test can be used to separate alkanes and alkenes? | the bromine water test because alkanes have no effect on bromine water while alkenes make it clear |
| What is combustion? | burning in oxygen |
| Do alkenes combust? | yes, but not as well as alkanes |
| Describe the combustion of alkenes. | they burn with a smokey, yellow flame because there is incomplete combustion |
| Why are alkanes preferred as fuels to alkenes? | alkenes release less energy per mole because there is incomplete combustion |
| Which is more reactive, alkanes or alkenes? | alkenes |
| Why are alkenes more reactive than alkanes? | because of the double bond in alkenes |
| What happens when alkenes react with other molecules? | the molecules 'add' to the alkene molecule across the double bond |
| What is an addition reaction? | a reaction in which two or more molecules react to become a single molecule |
| Write the equation for ethene reacting with bromine. |
 |
| What type of reaction is ethene with bromine? | an addition reaction |
| What is the general reaction of alkenes with halogens? |
All reactions with halogens follow the same pattern. The halogen atoms are added across the C=C bond which becomes a single bond  |
| Show the reaction of propene with bromine. | C3H6 + Br2 → C3H6Br2  |
| What is the test for alkenes? | an alkene will decolourise orange bromine water |
| Why are alkenes called unsaturated compounds? | because of the C to C double bond, alkenes do not contain the maximum hydrogen atoms for a hydrocarbon |
| What is created when H2 is added to an alkene? | an alkane |
| How is an alkene made into a saturated compound? | by adding a H2 molecule across the double bond |
| What conditions are required to add H2 to an alkene? |
• 60 °C • nickel catalyst |
| Why is H2 added across the C=C bond in unsaturated oils? | to straighten the molecule and raise the melting point |
| What is the process of adding H2 to an alkene called? | hydrogenation |
| What is a practical use for hydrogenation? | H2 is added to vegetable oils to make solid margarine |
| How is ethanol made from ethene? | by reacting ethene gas with steam
|
| What is ethanol made from ethene used for? | as an industrial fuel or solvent |
| What is needed to make ethene react with steam? | a high pressure and temperature |
| What is the big challenge with reacting steam with ethene? | the reaction is reversible so ethanol will break down into ethene and steam |
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