hydrocarbons

?

crude oil

  • finite resource found in rocks
  • formed from the remains of sea animals and plants (trapped under rock sediments in highly pressurised conditions)
  • mixture of carbon compounds
  • nearly all of the compounds in crude oil are composed of hydrocarbons

alkanes

  • mostly make up crude oil
  • to fine the chemical formula of an alkane -> 2n+2 (for every n carbon)

e.g. if there are 16 hydrogen atoms in an alkane, how many carbon atoms are there?              (http://classconnection.s3.amazonaws.com/57/flashcards/517057/jpg/heptane1307993664621.jpg)16-2=14

14/2=7

C7H16

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properties of hydrocarbons

LONG CHAIN HYDROCARBONS;

  • bigger in size
  • higher boiling point
  • lower volatility                                volatility: tendency to turn into a gas
  • higher viscosity                                               viscosity: how runny it is
  • less flammable

SHORT CHAIN HYDROCARBONS;

  • smaller in size
  • lower boiling point
  • higher volatility
  • lower viscosity
  • more flammable
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fractional distillation

  • crude oil is heated and fed in near the bottom of the fractionating column
  • the temperature of the column decreases going up the column
  • the gases move up the column and the hydrocarbons condense when they reach the temperature of their boiling points
  • the fractions are collected as liquids at different liquids

hydrocarbons with the smallest molecules have the lowest boiling points(http://www.cyberphysics.co.uk/topics/energy/fractional_distillation_crudeoil.gif)

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combustion

complete combustion:

hydrocarbon+oxygen-->carbon dioxide+water

when hydrocarbons burn in plenty of air, they transfer lots of energy to their surroundings as the reaction is highly exothermic. in complete combustion, the carbon and hydrogen are completely oxidised.

incomplete combustion:

when there isn`t enough oxygen to fully oxidise the hydrogen and carbon (e.g. in an engine), carbon monoxide is also produced

hydrocarbon+oxygen(insufficient)-->carbon dioxide+carbon monoxide+water

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cracking

some of the heavier fractions from the fractional distillation of crude oil are not in high demand. they have long molecules and are thick liquids/ solids so make poor fuels. less useful molecules can be broken down into more useful, smaller molecules using cracking.

CRACKING IS:                                     (DUE TO THERMAL DECOMPOSITION)

  • heating the hydrocarbon to vapourise it                                
  • passing the long-molecule vapour over a hot catalyst
  • OR                                                                                                                         
  • mixing the vapour with steam and heating to a very high temperature

ALKANES VS. ALKENES:

  • alkenes are produced as a result of cracking
  • alkenes are unsaturated (contain at least one double bond between their carbon atoms, 2 fewer hydrogen atoms in their molecules)
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alkenes

  • alkenes are generally more reactive than alkanes
  • alkenes react with bromine water, which decolourises the orange water

A POSITIVE TEST FOR UNSATURATED HYDROCARBONS IS THAT THEY TURN ORANGE BROMINE WATER COLOURLESS

alkanes dont react in bromine water.

(http://68.media.tumblr.com/a253cb4ba54acec7479b0ebf0d40629d/tumblr_inline_n2ldwoUwIT1syyfyn.png)

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alkane names

(http://chemistry-davincent.wikispaces.com/file/view/alkanes1.jpg/79657773/537x339/alkanes1.jpg)

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Comments

15JORDK

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thanks this is helpful

gabby

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not helpful at all! 

too much on one card, makes it harder to remember 

information on alkenes and alkanes is very poor. 

I would not recommend these revision cards 

Rabdul

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The test and the links do not work

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