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AQA A-Level Chemistry (new spec) 3.2 Alkanes
Terms in this set (33)
Define petroleum fraction
A mixture of hydrocarbons with a similar chain length and boiling point range
What is crude oil?
A mixture consisting mainly of alkane hydrocarbons
What is fractional distillation?
A physical process that separates fractions and involves splitting of weak VDW forces
Describe the process of fractional distillation
Oil preheated and passed into a fractionating column, the fractions condense at different heights, with smaller molecules condensing at the top and larger molecules condensing at the bottom. The temperature of the column decreases going up. Similar molecules condense at similar heights
What does vacuum distillation do?
Allows heavier fractions to be separated further without high temperatures
The conversion of large less useful hydrocarbons into useful hydrocarbons by breakage of C-C bonds
What are the advantages of cracking?
Shorter chain hydrocarbons are in higher demand, supply of shorter chain hydrocarbons can match the demand, shorter chain hydrocarbons are more valuable than the longer chain
What are the conditions for thermal cracking?
What are the products formed from thermal cracking
Alkenes and shorter chain alkanes
What are the conditions for catalytic cracking?
Slight pressure, 450°C, zeolite catalyst
What are the products formed from catalytic cracking?
Branched alkanes and cyclic alkanes
Why is catalytic cracking cheaper than thermal cracking?
Because it uses lower temperatures and pressures
Releases heat energy when burned
What are the only 2 products released after complete combustion?
Carbon dioxide and water
Why are alkanes used as fuels?
Because alkane combustion is highly exothermic
What causes incomplete combustion?
An insufficient supply of oxygen
How is CO bad for health?
How are unburned hydrocarbons bad for health?
What problems does solid carbon cause?
Makes asthma worse, damages lungs, causes breathing problems, smog, smoke and global dimming
Why is incomplete combustion inefficient compared to complete combustion?
It produces less energy per mole
What does sulfur dioxide and nitrogen oxides cause?
What do catalytic converters do?
Remove CO, NOx and unburned hydrocarbons from exhaust gases
What do catalytic converters do to the pollutants in exhaust gases?
Turn them into less harmful gases
2CO + 2NO --> 2CO2 + N2
What is the structure of a catalytic converter?
Ceramic honeycomb coated with a thin layer of metal
What does the honeycomb in a catalytic converter provide?
A larger surface area, leading to a faster reaction rate
What metals catalyse the reactions inside a catalytic converter?
Platinum, Palladium and Rhodium
What's wrong with the metals that catalyse reactions in a catalytic converter?
They're expensive and their extraction causes a lot of harm to the environment
What happens during flue gas desulfurisation?
SO2 is removed from waste gases produced in power station furnaces
What does flue gas desulfurisation involve?
Passing the sulfur dioxide through a calcium oxide scrubber
SO2 + CaO --> CaSO3
What product is produced from flue gas desulfurisation?
What can calcium sulfite be turned into?
Which greenhouse gases increase global warming?
CO2, H2O & CH4
Why do the greenhouse gases increase global warming?
Because they can re-emit IR radiation
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