C.4 Solar Energy In Biological Systems Flashcards
What is a conjugated system?
A series of alternating single and double bonds in a molecule.
What must a molecule contain to absorb light?
In order to absorb light in the visible region of the electromagnetic spectrum the molecule must contain a sufficiently long conjugated system. Molecules such as chlorophyll add carotenoids contain an extensive conjugated system and can absorb visible light.
How is photosynthesis important in converting energy?
Energy from the sun’s light is used in photosynthesis to produce carbohydrates such as glucose:
6CO2(g) + 6H20 (l) –> C6H12O6(aq) + 6O2(g)
Photosynthesis therefore converts light energy into chemical energy.
How can the products of photosynthesis be converted to ethanol?
The sugar/carbohydrate produced in photosynthesis can be fermented using yeast to make ethanol.
C6H12O6(aq) —-> 2C2H5OH(aq) + 2CO2(g)
Ethanol made via the fermentation of glucose from sugar cane can be used as a biofuel.
What happens in transesterification?
In transeseterification an ester is mixed with an alcohol and either a strong base eg NaOH or strong acid eg H2SO4 catalyst - the part of the ester from the alcohol is exchanged with the new alcohol.
What are some examples of transesterification products?
Transesterification of a triglyceride molecules eg in vegetable oil with methanol or ethanol yields a mixture of methyl/ethyl esters, glycerol and some free fatty acids.
Why are vegetable oils not used in internal combustion engines?
Although they contain a similar amount of energy per gram as conventional diesel fuel they are not used in internal combustion engines due to their very high viscosity.
How does transesterification help vegetable oils to be used as fuels?
Transesterification turns the triglyceride molecules (vegetable oil) into methyl and ethyl esters which have a much lower viscosity than the original oil - these are used as biodiesel.
Why can biodiesel flow more easily?
Biodiesel molecules have lower viscosity than vegetable oils because they have lower relative molecular masses and therefore weaker London forces between molecules. The weaker forces between the molecules allow them to flow more easily.
What are advantages of biofuels?
It is produced from renewable fuels
It contains no sulphur so it does not produce sulphur dioxide when burnt.
What are the disadvantages of biofuels?
They are more expensive than petroleum derived fuels
The land used to grow biofuel crops are not used to produce food crops which creates food shortages and a rise in food prices.
How are biofuels carbon neutral?
Biofuels are sometimes described as carbon neutral the carbon atoms in the biofuel came originally from CO2 in the atmosphere (photosynthesis) and only these are put back into the atmosphere when the fuel is burnt there is no net change in the number of CO2 molecules in the atmosphere.
