Alkanes

• Alkanes

  saturated hydrocarbons

  CnH2n+2

  cycloalkanes - CnH2n-2 hydrogens per carbon still saturated
• shape of alkane molecules

  always form tetrahedral shaper around carbon atom-109.5 degrees

  specific shape with specific angle because bonds repel each other equally bonds contain electrons so they will want to as far apart as possible
• Alkane shape and length

  bigger molecule or atom more induced dipole

  dipole forces as you have larger electron cloud

  no branching means molecules can pack together closely leading to more surface contact

  longer straight chain hydrocarbons have more induced dipole dipole forces so more energy needed to overcome forces means boiling point increase
• Branched hydrocarbons

  hydrocarbons with branches means they can't pack together as close weakening induced dipole dipole forces between the chains and lower boiling point
• complete combustion of alkanes

  alkanes burn in oxygen completely to form CO2 and water

  alkanes are good fuels most burn readily to produce large amounts of energy

  used to power vehicles electrically made using combustion of alkane
• complete combustion of butane

  
• using combustion equations

  when hydrocarbons burn we produce gases at the same temp and pressure we use volume ratio to these to work out the formula of hydrocarbons being burnt
• incomplete combustion of alkanes

  when alkanes burnt with limited supply of oxygen we produce carbon monoxide and carbon soot - incomplete combustion occurs
• incomplete combustion of butane

  
• carbon monoxide

  poisonous

  bonds to haemoglobin in blood and prevents oxygen bonding

  can be removed using catalytic converter

  soot causes - breathing problems

  makes buildings dirty and clog up energies
• free radical chain reaction

  3 stages initiation propagation and termination
• initiation

  radicals produced normally using visible light or uv

  called photochemical reactions

  bond breaks producing 2 radicals
• propagation

  radicals reacts with non radical (molecule)

  new radicals created which then go on to react with other non radicals

  chain reaction
• termination

  when 2 radicals react forming non radical molecule ending chain reaction
• free radical substitution making halogenoalkanes

  initiation- sunlight breaks the cl-cl bond photodissociation

  bond breaks equally producing 2 highly reactive radicals

  propagation - 1) cl radical react with methane to make methyl radical .^CH3

  2)methyl radical reacts with cl2 molecule forming chloromethane and cl^. radical

  3)Cl radical can react with more methane

  termination - 2 radicals react to make stable non radical

  
• products of free radical reactions