Chemistry - Hydrocarbons

• What are the uses of fossil fuels

  natural gas

  Petroleum

  Coal
• what are the two advantages of fossils fuels

  variety of forms - matched to used due to fractional distillation

  available at all times - wind and solar have limited availability
• what are the 4 disadvantages of fossil fuels

  non-renewable

  greenhouse gas production

  acid rain

  carbon monoxide production
• describe this weakness of fossil fuels - non-renewable

  finite resource

  formation of fossil fuel takes millions of year

  will eventually run out
• describe this weakness of fossil fuels - greenhouse gasses

  combustion releases carbon dioxide

  absorbs radiation that emits in all directions and back to the surface of the earth - temperature rises

  climate change - rising sea levels / drought / after melting ice caps / extreme of weather
• describe this disadvantage of fossil fuels - acid rain

  combustion releases sulfuric and nitrogen - when reacted with oxygen and water - sulfuric acid and nitric acid

  both contribute to acid rain

  effect health - breathing problems

  decomposition of limestone / pollutes water supplies
• describe this disadvantage of fossil fuels - carbon monoxide production

  inadequate supply of oxygen creates carbon monoxide

  toxic - replaces oxygen in haemoglobin - we don’t receive enough oxygen - death
• what is requires and produced from the complete combustion of alkanes

  required - oxygen in excess / ignition

  produced - carbon dioxide and water
• what is required and produce from the incomplete combustion of alkanes

  required - lack of oxygen

  produced -carbon monoxide Or carbon and water
• how does the length of the hydrocarbon effect wether the combustion is complete or not

  longer the chain - the increases likihood that it burns with yellow smoky flame - incomplete

  should burn with a blue flame
• what is halogenation

  the use of UV light for alkanes and halogen to react

  do not react in the dark
• what are the three steps to Halogenation

  initiation

  propagation

  termination
• describe step one of halogenation - initiation

  starts the reaction

  UV light has enough energy to break bonds ( Cl-Cl)

  homiletic bond fission - when the bond is broken and each bond atom receives one of the bond electrons - radicals are formed

  radical - species that contain unpaired electrons and are very reactive
• describe the second step of halogenation - propagation

  uses a radical as a reactant to then from a radical as a product

  reaction continues as a chain reaction
• describe the third step of halogenation- termination

  propagation steps continue until two radicals meet

  this stops the reaction
• what is a reaction mechanism

  shows each stage of the reaction progress - all stages
• what is a substitution reaction

  when an atom/group is replaced by another atom / group
• What is hydrogenation

  The addition of hydrogen across a double bond in order to break the double bond
• what are conditions for hydrogenation

  regent - hydrogen

  required - heat

  catalyst - nickel metal

  type for reaction - addition
• why is hydrogenation used

  commercially

  turns liquid vegetable oils into saturated solid fats ( margarine )
• what is an electrophile

  species that can accept a lone pair of electrons

  alkene are very susceptible to electrophiles due to the pi orbital pair of electrons
• describe electrophilic addition reactions

  type of addition reactions for alkenes

  uses a heterolytic bond fission mechanism

  meaning - when the bond is broken , one of the bonded atoms receives both of the bonded electrons
• Describe this example electrophilic addition reaction

  1 - permanent dipole of the HBr attacks the pi bond with delta + of the H as it is near the negative area. Electrons move from double bond to H and the HBr electrons moves to Br

  2 - formation of immediate carbocation and a bromine ion

  3 - the bromine ion is attracted to the carbocation - forms 2-bromoethane

  
• what are the types of carbocation

  primary - + on first atom

  secondary - + on the second atom

  second is more common as the position of the + allows a more even spread of charge - makes it stable
• what is the test for alkenes

  bromine water

  electrophilic addition reaction - with a temporary dipole

  alkane - saturated - no change - stays brown

  alkene - unsaturated - change - brown to clear / colourless
• What is a polymerisation

  When alkene monomers can be joined together to form a long polymer molecule
• what is addition polymerisation

  when the double bond is used to join multiple alkene monomers
• what is required for a repeating unit

  brackets

  two end bonds through the brackets

  n after the brackets

  single bond
• what polymer is this and what is its properties and uses

  Poly(chloroethane ) - PVC

  Used - water pipes / waterproof clothing / insulating covering for electrical wires

  Properties - good insulator and waterproof

  
• what polymer is this and what is its properties and uses

  Polyphenylethane

  Polystyrene

  Hard / good insulator

  uses - household items needing strength or stabilising

  packing materials when holes have been created

  
• what polymer is this and what is its properties and uses

  Polypropene

  Rigid

  Used or food containers/ general kitchen equipment