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how do we get alkanes to react
free radical substitution
what does free radical substitution turn alkanes into
halogenoalkanes
define a mechanism
a reaction which takes place over several steps
what is stage one of free radical substitution
initiation
what does initiation of free radical substitution require
UV light
what is the role of UV light in chlorification
excites the electron, breaking the covalent bond
define radical
excited, unpaired electron
give the equation for the initial stage of free radical substitution
Cl2 —> 2Cl.
what is stage two of free radical substitution
propagation
give the two equations for propagation in chlorification of methane
Cl. + CH4 —> HCl + .CH3, .CH3 + Cl2 —> Ch3Cl + Cl.
define a chain reaction
where the product of one reaction is the reactant of another
What is the name for stage three of free radical substitution
termination
Give 3 equations as an example of termination in chlorification of methane
Cl. + Cl. —> Cl2, .CH3 + Cl. —> CH3Cl, .CH3 + .CH3 —> C2H6
How does the reaction end
randomly, cannot be forced
What must the products of free radical substitution not be
radicals
define complete combustion
sufficient amounts of oxygen to fully react
what is the formula for complete combustion
alkane + oxygen —> carbon dioxide + water
define incomplete combustion
insufficient oxygen to fully react
what is the formula for incomplete combustion with limited oxygen
alkane + limited oxygen —> carbon monoxide + water
what is the formula for incomplete combustion with very limited oxygen
alkane + very limited oxygen —> carbon + water
what is carbon monoxide
a toxic, orderless and colourless gas
what is carbon
a black solid
what is a use of alkanes
for fuel
name some pollutants
CO, C, NO
why are alkanes generally used as fuel
that are generally unreactive
define global warming
increase in average temperature of the earth’s surface
what are causes of global warming
CO2, CH4, water vapour
define acid rain
acidification of water
what pH is acid rain
5-6
what is the cause of acid rain
sulfur dioxide (SO2)
what are the two formulas for sulphuric acid
H2SO3, H2SO4
define global dimming/smog
harmful and toxic chemicals in the atmosphere
what are causes of global dimming and smog
NOx, carbon particulates and unburnt hydrocarbons
how could we prevent acid rain
reacting a base with sulfur dioxide
how do we prevent acid rain (IRL)
filter sulfur dioxide through calcium oxide
write an equation for prevention of acid rain
CaO + SO2 —> CaSO3 + CaSO4
what is calcium oxide
lime
how can we reduce CO and NO emissions
catalytic converters
what elements do catalytic converters usually contain
metals such as Pt or Rh
how do we maximise rate at a low cost with catalytic converters
small amount of catalyst over a large surface area
write the equation for a catalytic converter
NO + CO —> CO2 + ½ N2
what are alkanes
saturated hydrocarbons
what does saturated mean
single carbon-carbon bonds
what are hydrocarbons
something containing hydrogens and carbons
what is petroleum
crude oil
what is crude oil
a mixture of mainly alkanes
how can you seperate crude oil into fractions
fractional distillation
define fractional distillation
continual evaporation and condensation of a mixture, causing separation of components due to different boiling points
what is the temperature gradient of a fractionating column
top is cooler than the bottom
what is the correlation between size and boiling point
smaller hydrocarbons have lower boiling points
what boiling points do molecules at the top have
lower boiling points
what is the formula for an alkane
CnH2n+2
what functional group do alkanes have
C-C single bonds
What boiling point do alkanes have and why
low due to weak Van Der Walls
what is the trend in alkane’s boiling points
increase with chain length
why do boiling points increase with chain length
larger Mr means more Van Der Walls
what type of boiling points do straight chain alkanes have and why
higher boiling points as they can stack closer increasing Van Der Walls
what does cracking do
breaks longer hydrocarbons into shorter alkanes and alkenes
how does cracking separate longer hydrocarbons
breaking C-C bonds
what two types of cracking are there
thermal and catalyst
why do we do cracking
short-chained molecules are typically more useful and more in demand
what are two requirements for thermal cracking
very high temperature, high pressure
what is the product of thermal cracking
short alkanes and alkenes
what are the two requirements for catalytic cracking
high temperature, zeolite crystal catalyst
what does catalytic cracking produce
alkanes and aromatic compounds
why may catalyst cracking be more effective
it cuts costs as the reaction can be done at a lower temperature and pressure and is quicker
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