Alcohols Flashcards
Primary, secondary, and tertiary alcohols
Intermolecular forces between alcohol molecules
In an alcohol, O is more electronegative than H - the O-H bond is polar with O being delta - and H being delta +.
This results in hydrogen bonding between molecules
Comparison of the boiling point of an alcohol with its alkene equivalent
Alcohols have Hydrogen bonding between molecules whereas alkenes have much weaker van der walls forces between molecules. More energy is required to overcome the strong Hydrogen bonds - alcohols have a higher boiling point
For a substance to be soluble in a given solvent, what needs to exist between solute and solvent molecules.
How does this apply to water and alcohols
Solute and solvent must have similar intermolecular forces.
Both alcohols and water consist of hydrogen bonds allowing alcohols to hydrogen bond with water
Methods of ethanol production
Fermentation of sugar
Hydration of Ethene
Methods of ethanol production - Fermentation
Reaction:
Glucose -> Ethanol + CO2
C6H12O6 -> 2C2H5OH +2CO2
Catalyst - Yeast
Plant sugar solution is used as glucose as plants can be regrown making it renewable
Anaerobic condition
37C is optimum temp. for enzymes
Low energy needed
Low cost
Rate of reaction: Slow - takes several days
Product quality: Impure - 15% ethanol max
Type of process - A batch process. Everything is put into a container and then left until fermentation is complete.
That batch is then cleared out and a new reaction set up. This is inefficient.
Methods of ethanol production - Hydration of ethene
Ethene + Steam -> Ethanol
C2H4 + H2O(g) -> C2H5OH
Catalyst - H3PO4
300C temp
70 atm
High energy needed
High cost
Rate of reaction: fast
Product quality: pure - 97% ethanol
Type of process - A continuous process - A stream of reactants is passed continuously over a catalyst. This is more efficient
How to make hydration of ethene more cost effective
The unreacted Ethene and water can be separated from the ethanol and can be reacted again
Why is biofuel thought to be more sustainable than fossil fuels.
More plants can be grown to replace the ones used to make biofuel making biofuel renewable - better than fossil fuels which are non renewable.
Why is biofuel thought to be carbon neutral
Plants carry out photosynthesis absorbing 6 moles of CO2 and producing 1 mole of glucose for the plants.
This glucose can be taken from plants and can be fermented with yeast producing 2 moles of ethanol and 2 moles of CO2.
These 2 moles of ethanol candies be combusted to release energy and 4 moles of CO2.
In total, 6 moles of CO2 are absorbed by the plant, and 6 are released back into the atmosphere.
Why is biofuel actually not carbon neutral
Energy is needed to produce biofuels:
Planting and harvesting crops - Fuel burnt in tractors and combine harvesters
Transportation of crops to production site - lorries burn diesel releasing CO2
Distillation to concentrate ethanol to make it suitable for use as a fuel - large amount of energy needed for this (this energy mat come from burning fossil fuels)
Clearing land to make it suitable for crop production - removes trees which store CO2 - burning them releases this into the atmosphere.
