Friday 5th September
TODAY WE ARE
LEARNING ABOUT
 How do alkenes differ from alkanes?
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  • _ns_t_r_t_d  
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    Key Questions:

    1. What is the structure of an alkene like?
      • Alkenes are hydrocarbons (molecules made up of only hydrogen and carbon) with a double carbon-carbon bond.
    2. What is the general formula for the homologous series of alkenes?
      • The general formula for the homologous series of alkenes is CnH2n.
    3. Why are alkene molecules called unsaturated molecules?
      • Alkene molecules are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms.
    4. What are the conditions for the addition of water to alkenes?
      • The conditions for the additional of water to alkenes is to use steam passed over a catalyst of hot phosphoric acid. The resulting product is an alcohol.
    5. What are the conditions for the addition of halogens to alkenes?
      • If the alkene is a gas the halogen must also be a gas. If the alkene is a liquid then the halogen can be bubbled through as a gas.
    6. What are the names of the first four members of the homologous series of alkenes?
      • The first four members of the homologous series of alkenes are ethene, propene, butene and pentene.
    7. What is the structural and display formula ethene?
      • The structural formula for ethene is C2H4, display formula shows C=C with 2 hydrogens bonded to each C by a single bond.
    8. What is the structural and display formula pentene?
      • The structural formula for ethene is C5H10, display formula shows one C=C anywhere with all other carbons single bonded C-C. There are 10 carbons single bonded, each carbon has four bonds in total.
    9. What is the functional group for alkenes?
      • Alkenes are hydrocarbons with the functional group C=C.
    10. What determines the reactions of organic compounds?
      • It is the generality of reactions of functional groups that determine the reactions of organic compounds.
    11. How does the combustion of alkenes differ in oxygen and in air?
      • Alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons, but they tend to burn in air with smoky flames because of incomplete combustion.
    12. How do alkenes react with hydrogen, water and the halogens?
      • Alkenes react with hydrogen (in the presence of a nickel catalyst), water (phosphoric acid catalyst) and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond.
    13. What are the conditions required for the addition of hydrogen to alkenes?
      • The conditions for the addition of hydrogen to alkenes is 300oC and over a heated catalyst of finely divided nickel
    14. What are the conditions required for the addition of water to alkenes?
      • The conditions for the addition of water to alkenes is high temperature (for steam) and a phosphoric acid catalyst.
    15. What are the structures of the following products of alkene addition reactions: 1. dibromoethane 2. dichloroethane 3. ethanol 4. ethane
      • The structures of the following products of alkene addition reactions are: 1. dibromoethane = CH2BrCH2Br 2. dichloroethane = CH2ClCH2Cl 3. ethanol = C2H5OH 4. ethane = C2H6