chemistry unit2

• a fuel is a substance that burns in oxygen to produce energy
• the main fuels are coal, oil and gas, they are made up of hydrocarbons
• hydrocarbon molecules contain hydrogen and carbon only
• hydrocarbons are joined by covalent bonds
• homologous series is a group of compounds with the same general formula and similar chemical properties
• homologous series includes:

  alkanes

  alkenes

  cycloalkanes
• the general formula for alkanes is:

  CnH2n+2
• we use alkanes as fuels, the contain carbon to carbon single bonds and are saturated
• as the length of the alkane increases the melting and boiling points also increase
• 1. meth
  2. eth
  3. prop
  4. but
  5. pen
  6. hex
  7. hec
  8. oct
• the alkenes contain carbon to carbon double bonds and are unsaturated
• we use alkenes to make plastics
• the general formula for the alkenes are:

  CnH2n
• as the molecular size increases, the melting and boiling points also increase as the inter molecular bonds get stronger
• an unsaturated molecule contains at least one carbon to carbon double bond
• a saturated molecule contains carbon to carbon single bonds only
• alkenes decolourise bromine solution rapidly as the contain carbon to carbon double bonds
• bromine water can be used to distinguish between an alkane and alkene, as an alkene decolourises bromine water and an alkane does not
• solid= mp and bp bigger than temp

  liquid= mp lover than bp, bp bigger than temp

  gas= mp and bp lower than temp
• the cycloalkanes are saturated and contain carbon to carbon single bonds
• the general formula for cycloalkanes is:

  CnH2n
• isomers have the same molecular formula but different structural formulas
• addition reactions occur when the double bonds in an alkene break open and a smaller molecule adds on the the carbons where the double bond was
• hydrogenation turn ethene into ethane by adding hydrogen across the double bond
• hydration turn ethene into ethanol by adding water across the double bond
• halogenation add a halogen element on the double bond such as bromination
• a fuel is a chemical which burns to give out energy
• combustion is when a substance burns in oxygen and energy is produced in the process
• a reaction in which energy is released is called an exothermic reaction
• incomplete combustion is when a fuel burns in a limited supply of oxygen and produces carbon monoxide instead of carbon dioxide
• when alkanes and alcohols combust they use up oxygen and form carbon dioxide and water
• we can record how much fuel is burned and also the change in temperature:

  Eh=c m ^T
• Eh= heat energy (kJ)

  c= 4.18

  m= mass of water (kg)

  ^T= change in temperature
• the alcohols form a homologous series very similar in structure to alkenes but their names end in ol
• the structural group of the alcohols is the hydroxyl group -OH
• the general formula of the alcohols:

  CnH2n+1 OH
• alcohols are used as fuels as they are highly flammable and burn with a clean flame, alcohols are often used as solvents
• methanol, ethanol and propanol are miscible with water, thereafter the solubility decreases as size increases
• carboxylic acids contain the carboxyl functional group -COOH
• the carboxylic acids names end in oic acid