Alkanes Flashcards
Why are alkanes called saturated hydrocarbons?
Because they don’t contain double carbon bonds.
How are the alkanes from crude oil removed?
Fractional Distillation
How does fractional distillation work?
- The crude oil is vaporised at high temperatures.
- The vaporised crude oil goes into the fractionating column and starts to rise.
- The hydrocarbons with higher boiling points remain at the bottom because they don’t vaporise well.
- The hydrocarbons with the lower boiling points rise and they cool and condense. They then are collected as a fraction.
5, Because the alkanes have different boiling points they condense at different temperatures and can be collected at different fractions.
What is cracking?
The breaking of long-chain alkanes into smaller hydrocarbons.
What are the commercial benefits of cracking?
Smaller hydrocarbons are more in demand so they are more valuable.
What are the conditions needed for thermal cracking?
- High temperatures 400 to 900 degrees
- High pressures up to 70atm
What does thermal cracking produce?
smaller alkanes and alkenes
What are the alkenes produced in thermal cracking used for?
They are used to make polymers and ethanol.
What conditions are needed for catalytic cracking?
- zeolite catalyst
- moderate pressure.
- temperature of 450 degrees
What does catalytic cracking produce?
- aromatic hydrocarbons
- branched and cyclic alkanes
What is the use for the cyclic hydrocarbons produced in catalytic cracking?
They burn more cleanly so they are used as fuels.
Why is catalytic cracking the preferred method of cracking?
It requires a lower temperature which means less energy needs to be used and that saves money.
What is produced in the complete combustion of alkanes?
carbon dioxide and water.
What is produced in the incomplete combustion of alkanes?
carbon monoxide, sometimes carbon and water
What are the environmental consequences of the formation of nitrogen oxides?
Nitrogen oxide is toxic and it can form acidic nitrogen dioxide gas. Nitrogen dioxide is toxic and it can lead to the formation of acid rain.
What are the environmental consequences of the formation of carbon monoxide?
It is toxic
What are the environmental consequences of the formation of carbon dioxide?
contributes to global warming
What are the environmental consequences of the formation of unburnt hydrocarbons?
contribute to the formation of smog in the atmosphere
What are the environmental consequences of the formation of soot ( C )?
contribute to global dimming and respiratory problems.
How is sulfur dioxide removed from flue gases?
It reacts with carbon oxide to form carbon sulfite which removes the sulfur dioxide from the gases.
What is the role of catalytic converters?
They remove carbon monoxide, nitrogen oxides and unburnt hydrocarbons from exhaust gases by turning them into relatively unharmful carbon dioxide, nitrogen and water.
How does carbon monoxide contribute to global warming?
They absorb infrared radiation and they emit some of the energy back to the earth which keeps it warm.
What is the mechanism to make halogenoalkanes from alkanes?
free radical substitution
What is a free radical?
a species that has an unpaired electron.
What conditions do you need for free radical substitution?
UV light
