hydrocarbons

• what are hydrocarbons?

  organic compouns made of carbon and hydrogen.
• in alkanes, how many atoms to carbon atoms bond to?

  4
• why are alkanes called saturated hydrocarbons?

  as all their bonds with other atoms are single bonds.
• what are the uses of alkanes?

  they have quite low reactivity but they combust quite well which makes them useful as fuels.
• what is the general formula for alkanes?

  CnH(2n+2)
• what are the dominant compounds in crude oils?

  Hydrocarbons
• what are the 4 smallest alkanes in ascending order?

  • methane (CH4)
  • ethane (C2H6)
  • propane (C3H8)
  • butane (C4H10)
• what is a homologous series?

  a series of compounds with the same general formula.
• what is the general formula for alkenes?

  CnH2n
• what are alkenes?

  hydrocarbons with a C=C double bond.
• what is more reactive, alkanes or alkenes?

  alkenes
• why are alkenes more reactive than alkanes?

  the presence of the C=C functional group
• why are alkenes called unsaturated hydrocarbons?

  they contain a double bond between 2 of their carbon atoms
• how will an alkane and an alkene with the same length of carbon chain be different?

  they will have different numbers of hydrogen atoms, the alkane will have 2 more hydrogen atoms.
• what are the 4 shortest alkenes in ascending order?

  • ethene (C2H4)
  • propene (C3H6)
  • butene (C4H8)
  • pentene (C5H10)
• what happens during addition reactions for alkenes?

  the C=C bond opens up and allows carbon atoms to bond with new atoms.
• which hydrocarbon will react when shaken with bromine water?

  alkenes
• how do alkenes react with bromine water?

  causes the solution to change colour from orange-brown to colourless.
• what test can be used to distinguish alkenes from alkanes?

  Bromine water test
• when reacting alkenes with steam, what needs to be present for alcohol to be formed?

  a phosphoric acid catalyst.
• when alkenes are involved in combustion reactions with oxygen, wy do they burn with smoky flames?

  their combustion is incomplete.
• when can alkanes be formed by combining hydrogen with an alkene?

  when a nickel catalyst is present.
• what is adding hydrogen atoms across a carbon-carbon double bond called?

  hydrogenation.
• what is formed when alkanes are burned without enough oxygen?

  carbon monoxide
• what properties does carbon monoxide have?

  • colourless
  • toxic
  • odourless
• what does the combustion (burning) of hydrocarbon when there is a good air supply involve?

  • energy release
  • the oxidation of carbon and hydrogen to create carbon dioxide and water.
• why do short-chain hydrocarbon fractions burn easily?

  • they are highly volatile
  • they ignite easily
  • they have low boiling points
• what is a functional group?

  a group of atoms that determines the nature of the reactions of an organic compound.
• what do alkenes and alkanes do in combustion reactions?

  burn
• during complete combustions, what happens to alkenes and alkanes?

  they are oxidised to form carbon dioxide and water.
• why are alkanes useful as fuels?

  they have quite low reactivity, but they combust quite well.
• what does alkanes being saturated mean?

  being saturated means that the molecule only connects to other atoms with single bonds. So, each of the carbon atoms in an alkane has a bond to 4 more atoms.
• what is the formula for methane?

  CH4
• what is the formula for ethane?

  C2H6
• what is the formula for propane?

  C3H8
• what is the formula for butane?

  C4H10
• what are the features of alkenes?

  • unsaturated
  • general formua: CnH2n
  • reactive
• what is the formula for ethene?

  C2H4
• what is the formula for propene?

  C3H6
• what is the formula for butene?

  C4H8