Alkanes

• Alkanes


  saturated hydrocarbons
• main constituent of crude oil is alkanes
• only intermolecular force in alkanes

  van der waals
• short chain alkanes are gases when?

  at room temperature and pressure
• Alkanes with more than 18 Carbons are

  waxy solids at room temperature and pressure
• Pentane is a liquid with a low boiling point
• alkanes are insoluble in water why?

  hydrogen bonds in water are stronger than the vdw in alkanes
• bond angle of non cycloalkanes

  109.5°
• bond angles in are _____ in cycloalkanes than non cycloalkanes


  smaller
• polarity of alkanes


  non-polar because of weak van der waals forces
• trend boiling point of alkanes

  (Very low) as molecules get larger, boiling point increases
• branched alkanes have a lower boiling point than unbranched why?

  weaker van der waal’s forces, lower surface area of contact
• alkane solubility


  insoluble in water
• alkanes are insoluble in water why?

  alkanes are non polar and non polar substances don‘t dissolve well in water (polar solvent)
• alkanes are unreactive because…

  C-C bonds are strong
• Alkane uses


  fuels, lubricant, making other organic molecules
• why is fractional distillation a physical process?

  no covalent bonds are broken
• alkane at the bottom of the colomn

  Bitumen (C70)
• properties of shorter alkanes compared to longer alkanes

  lower boiling points

  more volitile

  more flammable

  less viscous

  less coloured
• shorter alkanes are what state at room tempe and pressure


  gases and liquids
• reasons for cracking


  • Higher demand for haptha/ petrol
  • Low demand for larger alkanes
• conditions of thermal cracking

  high temperature

  high pressure
• thermal cracking produces


  high percentage of alkenes
• origin of crude oil

  formed million of year ago by the breakdown of plant and animal remains at high pressures high pressure deep below the surface of the earth generally with low amounts of oxygen
• element other than hydrogen and carbon that crude oil contains

  sulfur
• NO, NO2, N2O4 all dissolve in water to give…

  HNO3
• affects of NO, NO2 and N2O4 on the environment 


  contribute to acid rain and photochemical smog
• SO2 contribution to pollution of the atmosphere

  dissolves in water to give H2SO4 (acid rain)
• negative effects of C particulates

  asthma/ cancer causing
• CO2 contribution to pollution of the atmosphere

  greenhouse gas

  increased levels of CO2 lead to global warming and climate change
• unburnt alkanes contribution to pollution of the atmosphere

  greenhouse gases, global warming, climate change
• internal combustion engine produces a number of pollutants including

  NOx, CO, C, unburnt hydrocarbons
• gaseous pollutants from internal combustion engines can be removed using

  catalytic converters