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define petroleum fraction
mixture of hydrocarbon with a similar chain length and boiling point range
state the stages of how fractional distillation works (9)
oil is pre heated
then passed into column
the fractions condense at different heights
the temperature of the column decreases upwards
the separation depends on boiling points
boiling point depends on size of molecules
similar molecules condense together
small molecules condense at the top at lower temps
and big molecules condense at the bottom
state the process of vacuum distillation unit (2)
heavy residue from the fractionating column are distilled again under a vacuum
lowering the pressure over a liquid will lower its boiling point
what is vacuum distillation used for (2)
allows heavier fractions to be further separated
without high temperatures which could break them down
define cracking (1)
conversion of large hydrocarbons to smaller hydrocarbon molecules by breaking the C-C bonds
what are the economic reasons for cracking (3)
the petroleum fractions with shorter C chains are more in demand than larger fractions
to make use of excess larger hydrocarbons and to supply shorter ones
the products of cracking are more valuable than the starting materials
what are the conditions for thermal cracking (2)
high pressure = 7000 kPa
high temp = 400oC to 900oC
what are the conditions for catalytic cracking (3)
slight pressure
high temperature = 450oC
zeolite catalyst
what are the products of thermal cracking (2)
alkenes
sometimes hydrogen
what are the products of catalytic cracking (2)
branched and cyclic alkanes
aromatic hydrocarbons
write the two equations for the production of SO2 (3)
S + O2 = SO2
CH3SH+ 3O2 = SO2 + CO2 + 2H2O
explain how sulfur can be removed from the waste gases from furnaces (3)
the gases pass through a scrubber containing basic calcium oxide
which reacts with the acidic sulfur dioxide
in a neutralisation reaction
write the equation for neitralising sulfur dioxide (2)
SO2 + CaO = CaSO3
what is the product from neutralising sulfur dioxide (1)
calcium sulfite
write the equations for production of nitrogen oxide (2)
N2 + O2 = 2NO
N2 + 2O2 = 2NO2
how is nitrogen oxide released from car engines (1)
the high temperature and spark in the engine provides sufficient energy to break the N2 bonds
what is the environmental consequence of nitrogen oxide (1)
is toxic and cam form acidic gas NO2 which can form acid rain
what is the environmental consequence of carbon monoxide (1)
toxic
what is the environmental consequence of carbon dioxide (1)
contributes towards global warming
what is the environmental consequence of unburnt hydrocarbons (1)
contributes towards formation of smog
what is the environmental consequence of soot(1)
global dimming
what are catalytic converters (1)
remove CO and NO and unburned hydrocarbons from exhaust gases to turn them into harmless products
write the equation for the conversion of CO and NO into harmless products (1)
2 CO + 2 NO = 2 CO2 + N2
write the equation for the conversion of hydrocarbons and NO into harmless products (2)
C8H18 + 25 NO = 8 CO2 + 12½ N2 + 9 H2O
explain the mechanism of greenhouse effect (5)
UV wavelength radiation passes through the atmosphere to the earths surface and heats it up
earth radiates out infrared long wavelength radiation
the C=O bonds in CO2 absorb infrared radiation
so the IR radiation does not escape from the atmosphere
this energy is transferred to other molecules in the atmosphere via collision so the atmosphere is warmed
write the equation for the reaction of alkanes with chlorine (1)
CH4 + Cl2 = CH3Cl + HCl
what is the mechanism used to react alkanes with halogens (1)
free radical substitution
write the initiation step for the reaction of alkanes with chlorine (1)
Cl2 = 2Cl.
what is used to make initiation happen (1)
UV light
write the propagation steps for the reaction of alkanes with chlorine (2)
CH4 + Cl. = HCl + .CH3
.CH3 + Cl2 = CH3Cl + Cl.
write the termination steps for the reaction of alkanes with chlorine (2)
.CH3 + Cl . = CH3Cl
.CH3 + .CH3 = CH3CH3