2.5 - Hydrocarbons Flashcards
What is a fossil fuel?
A source of energy that is derived from organisms that lived a long time ago.
What is a non-renewable resource?
Resources that cannot be reformed in a a reasonable time scale.
What is a green house gas?
One that causes an increase in the Earths temperature.
What are 2 advantages to using fossil fuels?
They are available in a variety of forms so that the type of fuel can be matched with its use
They are available at all times (green sources like solar have limited daily availability)
What are the 4 disadvantages of using fossil fuels?
They are non-renewable
Combustion of fuels creates CO2 (a green house gas)
Acid rain forms from sulfur and nitrogen
Carbon monoxide formation which is toxic to haemoglobin as it acts as an inhibitor
What is the equation for alkanes?
CnH2n+2
Are alkanes saturated or unsaturated?
Saturated
What state is a small alkane?
Gas (natural gas like methane)
What state is a large alkane?
Liquids (petrol)
What state is the largest alkane?
Solids (wax)
Why are alkanes generally unreactive?
They are non-polar.
What is complete combustion?
If sufficient oxygen is present, carbon dioxide and water are formed.
What is incomplete combustion?
If insufficient oxygen is present, carbon monoxide and water are formed.
What is halogenation?
The reaction between an organic compound and any halogen.
Basically free radical substitution.
What is the trigger for free radical sub/halogenation?
UV light, will not react in darkness
What is the first stage in free radical substitution?
Initiation
- starts the reaction
- UV light has enough energy to break the cl-cl bond homolytically
- homolytic bond fission occurs when each of the bonded atoms recieves one of the bond electrons so that radicals are formed
- this means they are highly reactive
Cl2 = Cl+Cl
What is the second stage in free radical substitution?
Propagation
- uses radicals as a reactant and then forms a radical as a product
- chain reaction
Cl* + CH4 = CH* + HCl
CH* + cl2 = Ch3Cl + Cl*
What is the final stage in free radical substitution?
The propagation steps continue until 2 radicals meet
Cl* + Ch3* = Ch3Cl
Are alkenes saturated or unsaturated?
Unsaturated as they contain a double bond
What is the formula for an alkene?
CnH2n
How can alkenes be formed in industry?
By cracking petroleum, which is important in polymerisation reactions
What does the double bond create for an alkene?
An area of electron density, called a Pi orbital
A double bond means high reactivity
What is an electrophilic addition reaction?
- as alkenes have a pi bond, they are suseptible to an attack by an electrophile
- the mechanism involves heterolytic bind fission leading to an addition reaction
What is an electrophile?
Any species that can accept a lone PAIR of electrons
What is heterolytic bond fission?
When a bond is broken and one of the bonded atoms recieves both of the bonded electrons
What are the triggers for electrophilic reactions?
A double bonded alkene and an electrophile
What happens to electrophiles in electrophilic reactions that are non-polar?
A dipole is induced by the negative charge in the pi bond.
What are the 2 common uses of electrophillic addition?
Bromine - alkene testing
Hydrogen - hydrogenation
How is bromine linked to electrophillic addition?
- testing for an alkene
- bromine is brown, turns colorless when an alkene is present
- bromine water is used instead of bromine liquid as b.l is very corrosive
How is hydrogen linked to elctrophillic addition?
- hydrogenation
- catalysed by transition metals
- the reaction is important in industry because liquid oils contain many double bonds that can be saturated with hydrogen to form solid products like butter
Why are secondary and tertiary carbocations more desirable than primary carbocations?
- alkyl groups tend to release electrons so that they become delta positive
- this spreads or delocalises the positive charge and stabilises the ion
- this means 2/3 carbocations are more stable than 1* cations, thus are the more desirable/common product
What is polymerisation?
Joining of a very large number of monomer molecules to make a large polymer molecule
What is addition polymerisation?
- occurs in alkenes
- the double bond is used to join molecules
-example when ethene is polymerised, poly(ethene) is formed
Drawn n c=c ——— (c-c)n
What is poly(propene)?
Monomer propene
Polymer poly(propene)
polypropene is rigid and used in food containers and general kitchen equipment
What is poly(chloroethene)?
Monomer chloroethene
Polymer polychloroethene
Old name vinyl chloride, or polyvinyl chloride (PVC)
Used in water pipes, waterproof clothing, insulating cover for electrical cables
What is poly(phenylethene)?
monomer phenylethene
polymer poly(phenylethene)
Old name styrene, poly styrene
Hard, used in household items for strength and integrity
