Alkanes Flashcards
describe the key points of fractional distillation
Oil is pre-heated
* then passed into column. * The fractions condense at different heights
* The temperature of column decreases upwards
* The separation depends on boiling point. * Boiling point depends on size of molecules. * The larger the molecule the larger the van der waals forces
* Similar molecules (size, bp, mass) condense together
* Small molecules condense at the top at lower temperatures
* and big molecules condense at the bottom at higher temperatures.
describe what cracking is
conversion of large hydrocarbons to smaller hydrocarbon molecules by breakage of C-C bonds
why is cracking important
The petroleum fractions with shorter C chains (e.g. petrol are in more demand than larger fractions.
describe the conditions for thermal cracking
High pressure (7000 kPa)
High temperature (400°C to 900°C)
what is produced from thermal cracking
produces mostly alkenes e.g. ethene used
for making polymers and ethanol
e.g
C8H18 -> C6H14 + C2H4
what are the conditions for catalytic cracking
Conditions:
Slight or moderate pressure
High temperature (450°C)
Zeolite
what is normally produced from catalytic cracking
Produces branched and cyclic
alkanes and aromatic hydrocarbons
cheaper than thermal cracking because less energy is used
why are alkanes good fuels
they readily burn completely in the presence of oxygen
they are highly exothermic
describe flue gas desulfurisation
flue gas desulfurisation removes SO2 from the waste gases in furnaces .
The gases pass through a scrubber containing basic calcium oxide which reacts with the acidic sulfur dioxide in a neutralisation reaction.
SO2 + CaO –> CaSO3
how is nitrogen oxide formed
Nitrogen oxides form from the reaction between N2 and O2
inside the car engine.
The high temperature and spark in the engine provides sufficient energy to break strong N2 bond
what is the role of catalytic converters
These remove CO, NOx and unburned hydrocarbons (e.g. octane, C8H18)
from the exhaust gases, turning them into ‘harmless’ CO2
, N2 and H2O.
write equation for the reaction in a catalytic converter
2 CO + 2 NO –>2 CO2 + N2
C8H18 + 25 NO –>8 CO2 + 12½ N2 + 9 H2
describe a catalytic converter
Converters have a ceramic
honeycomb coated with a thin
layer of catalyst metals
platinum, palladium, rhodium
– to give a large surface area.
.
describe the greenhouse effect
UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
The Earth radiates out infrared long wavelength
describe the formation of halogenoalkanes
In the presence of UV light alkanes react with chlorine to form a
mixture of products with the halogens substituting hydrogen atoms
