alkanes

• what is complete combustion?

  burning a substance completely in oxygen, produces carbon dioxide and water only
• what is incomplete combustion?

  burning a substance in a limited supply of oxygen, produces carbon monoxide and water
• what is a hydrocarbon?

  compound containing hydrogen and carbon atoms only
• what does saturated mean?

  containing single bonds only
• what is a homologous series?

  same functional group
• what is a structural isomer?

  same molecular formula but different structural formula
• what is a radical?

  a species with an unpaired electron
• what is a substitution reaction?

  a reaction in which an atom or group of atoms is replaced with another atom
• what is homolytic fission?

  the breaking of a covalent bond where the shared pair of electrons are split equally forming two radicals
• which intermolecular force forms between alkanes?

  - london forces formed by the electtrons moving around

  - induces a temporary dipole from an uneven distribution of electrons
• what happens to the boiling point as the chain length of alkanes increases?

  - more points of contact between molecules

  - more intermolecular temporary dipole-dipole forces between the molecules

  - more energy needed to break

  - boiling point increases
• what is fractional distillation?

  separation of liquid mixture by its boiling point
• explain the process of fractional distillation?

  - vaporises crude oil

  - the gases rise until they hit the temperature where their boiling point is

  - vaporise and condense into liquid and collected as a fraction
• where will long chain alkanes be in the fractional distillation column?

  at the bottom as they have a high boiling point
• why do shorter alkanes make more useful fuels?

  - lower boiling points

  - less points of contact

  - weaker temporary dipole-dipole interactions

  - less energy needed to break
• what is catalytic cracking?

  breaking down of a long chain alkene into a more useful short chain hydrocarbon
• what is isomerisation?

  - heating unbranched isomers to form branched chain isomers

  - lower boiling so more efficient fuel and easier to burn
• what is reforming?

  - removing the two end hydrogens to make cycloalkanes

  - lower boiling points so more efficient fuel so easier to burn
• what happens to the hydrogen by product in reforming?

  - used to make vegetable oil

  - used in the haber process to make ammonia
• why is the combustion of fuels an effective energy source?

  - highly exothermic reaction so lots of heat energy produced
• why is incomplete combustion dangerous?

  - carbon monoxide is produced which is a toxic gas

  - in a confined environment it could be fatal
• how are nitrogen oxides made?

  - nitrogen and oxygen from the air react at high temperatures in combustion chamber

  - N2 + 02 = 2NO
• why are nitrogen oxides dangerous?

  - converted to nitric acid, contributes to acid rain

  - nitrogen dioxide reacts with unburned hydrocarbons to form smog
• how are unburnt hydrocarbons formed?

  released in vehicle exhaust
• why are unburnt hydrocarbons dangerous?

  - some are carcinogenic

  - react with nitrogen dioxide to form smog
• what are catalytic converters?

  honeycomb structure (cheaper, large sa so faste ror) coated in rhodium, palladium or platinum alloy.
• how to catalytic converters work?

  1) the harmful CO and NO molecules adsorb to the catalytic surface

  2) the CO and NO bonds are weakend

  3) converted to nitrogen and carbon dioxide

  4) the less harmful molecules desorb from the surface of the catalyst
• what is adsorption?

  when a weak temporary bond is formed with the surface (sticking to the surface)
• what is biofuel?

  fuel that is derived from recently living materials such as plants or the waste of animals
• is radical substitution a good method for the production of a single halogenoalkane?

  - no as there is a lot of waste

  - multiple termination steps

  - reaction is uncontrollable
• what is hydrolysis?

  the breaking of a bond by adding water
• what is a nucleophile?

  electron pair donor
• what is electronegativity?

  ability of an atom to attract electrons
• what is bond enthalpy?

  the enthalpy change when one mole of a bond in the gaseous state is broken
• what is bond polarity?

  a measure of how equally or unequally the electrons in any covalent bond are shared
• what is a substitution reaction?

  when an atom or group of atoms is replaced by a different atom or group of atoms
• what is electron deficiency?

  an atom with a slightly positive charge due to a covalent bond with a more electronegative atom
• what is reflux?

  the continuous boiling and condensing of a reaction mixture to ensure the reaction takes place but prevents the contents of the flask boiling dry
• what is volatility?

  the ease which a liquid turns into a gas
• why does the electronegativity of the halogens decrease down group 7?

  - larger nuclear charge

  - increased atomic radius

  - more shielding

  - weaker nuclear attraction for a bonding pair of electrons