Chemistry /Edexcel A Level Chemistry: 6: Organic Chemistry I Part 2
Edexcel A Level Chemistry: 6: Organic Chemistry I Part 2
This deck covers key concepts in organic chemistry, focusing on hydrocarbons, cracking, combustion, biofuels, and isomerism. It includes definitions, processes, and the implications of chemical reactions.
Why don't the largest hydrocarbons vaporise?
Their boiling points are too high
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Key Terms
Term
Definition
Why don't the largest hydrocarbons vaporise?
Their boiling points are too high
What happens to the vapour as it moves up the fractionating column?
It cools, and each fraction condenses at a different temperature
What happens to the hydrocarbons with the lowest boiling points?
The don't condense, they're drawn out as gases at the top of the column
How can the heaviest fractions be used?
They can be 'cracked' to form smaller molecules
What are the two types of cracking?
Thermal and catalytic
What are the conditions of thermal cracking?
1000 degrees C and high pressure (70 atm)
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| Term | Definition |
|---|---|
Why don't the largest hydrocarbons vaporise? | Their boiling points are too high |
What happens to the vapour as it moves up the fractionating column? | It cools, and each fraction condenses at a different temperature |
What happens to the hydrocarbons with the lowest boiling points? | The don't condense, they're drawn out as gases at the top of the column |
How can the heaviest fractions be used? | They can be 'cracked' to form smaller molecules |
What are the two types of cracking? | Thermal and catalytic |
What are the conditions of thermal cracking? | 1000 degrees C and high pressure (70 atm) |
What does thermal cracking produce? | Alkenes |
What is the catalyst in catalytic cracking? | Zeolite (hydrated aluminosilicate) |
What does catalytic cracking produce? | Aromatic hydrocarbons and motor fuels |
Why is catalytic cracking more beneficial? | It cuts costs, because lower pressure and temperature can be used and the reaction is sped up by the catalyst |
What can alkanes be reformed into? | Cycloalkanes and aromatic hydrocarbons |
What is knocking? | Where alkanes explode of their own accord when the fuel/air mixture in the engine is compressed |
What are the most likely hydrocarbons to cause knocking? | Straight chain ones |
What catalysts are used for reforming? | Platinum on aluminium oxide |
What state do fuels have to be in to undergo combustion reactions? | Gaseous |
Why do larger alkanes produce more energy per mole? | They have more bonds to break |
What are the issues with carbon monoxide? | Carbon monoxide is better at bonding with haemoglobin so less oxygen is carried around the blood stream, leading to oxygen deprivation, and this can be fatal |
What are the issues with SO2 and NOx? | Acid rain can be caused by the burning of fuels that contain sulfur, as the sulfur dioxide can be converted to sulfuric acid. Oxides of Nitrogen can also cause acid rain as they are converted into nitric acid |
What is the main issue with fossil fuels? | They are non-renewable |
What biofuels are available? | Bioethanol |
How is bioethanol made? | By the fermentation of sugar from crops such as maize |
How is biodiesel made? | By refining renewable fats and oils such as vegetable oils |
How is biogas made? | Produced by the breakdown of organic waste matter |
Why are biofuels classed as carbon neutral? | Because although they release CO2 when burnt, the plants took in CO2 as they grew. |
What are the problems with biofuels? | Petrol car engines have to be modified to use the fuel and land used to grow the crops then can't be used to grow food, an issue in developing countries |
What are sigma bonds? | Single covalent bonds |
When is a sigma bond formed? | When two orbitals overlap in a straight line, giving the highest possible electron density between two positive nuclei |
What does the high electron density between the nuclei mean for sigma bonds? | That there is strong electrostatic attraction and so sigma bonds are the strongest |
What is a pi bond? | The second part of a double bond, along with a sigma bond |
How are pi bonds formed? | When two lobes of two orbitals overlap sideways - one above and one below the molecular axis |
What is the electron density in a pi bond like? | Spread out, above and below the nuclei so the electrostatic attraction is weaker and they are more easily broken |
How do strengths of double and single bonds compare? | A double bond is less than twice as strong as a single bond |
Can double bonds rotate? | No |
Why can double bonds rotate? | Because the p-orbitals overlap in pi bonds |
What are Z-isomers? | When the same groups are either both above or both below the bond |
What are E-isomers? | When the same groups are on opposite sides, one above and one below the double bond |
How does E/Z isomerism work when all the groups are different? | The atoms with the larger atomic numbers are given priority |
What are cis isomers? | When the groups are on the same side of the double bond, eg both above or both below |
What are trans isomers? | When the groups are on different sides of the double bond, eg one above and one below |
When is E/Z isomerism used? | When there are two high-priority groups |