Agriculture and Industry notes

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Agriculture and industry notes
Nitrogen Cycle
o Almost all of the nitrogen in the soil is present in complex organic molecules and so is not
available to plants.
o However, various processes convert the unreactive atmospheric nitrogen and organic
nitrogen compounds into ammonium and nitrate ions which are available to plants.
o The main processes are shown in the nitrogen cycle below:
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Inorganic Fertilisers
o Today, more than half of the world's cereal production relies on inorganic fertilisers.
o Without fertiliser it would be near impossible to feed the world's population.
o The raw materials used to produce inorganic fertilisers are water, air, natural gas, phosphate
rock, potash rock and sulphur.
o There is a vast range of inorganic fertilisers; there are ammonium nitrate, ammonium
sulphate, ammonium phosphate, urea and potassium nitrate fertilisers.…read more

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Ammonia, due to the hydrogen bonding that occurs between its molecules, has a higher
boiling point than nitrogen and hydrogen. Thus the ammonia can be liquefied and tapped off
from the mixture as it is produced; this results in a greater yield of ammonia.
Pesticides
o Crops must compete successfully for resources in order to survive and produce a good yield.…read more

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DDT
o Fat soluble molecules are usually the most effective pesticides; because they are non-polar,
they are able to dissolve in the fatty tissues of the pest and so reach the sites of action
rapidly.
o However, their solubility in organic substances may cause them to accumulate and become
concentrated up the food chain; bio-accumulation.
o DDT was discovered in Germany, 1939; it has prevented millions of deaths from diseases
such as Typhus and Malaria.
o DDT is from the organochlorine insecticides.…read more

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Parathyroids
o The flowers from plants such as chrysanthemums contain their own
pesticides; they have been used for centuries as natural
insecticides.
o In the 1920's and 1930's, the structure of the natural insecticides
were worked out; for example, Pyrethrin 1:
o Pyrethrins are ideal insecticides in that they are powerful and are harmless to mammals
under normal circumstances.
o Unfortunately, the natural pyrethrins are unstable in light; they are of limited use in
agriculture due to their rapid breakdown.…read more

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How they work
o The pyrethroids work by binding to membrane proteins within the nerve cells of insects.
o Nerve cell membranes act as channels for the passage into and out of the cells; the
pyrethroids work by penetrating the nerve cell membrane, blocking open the sodium
channels; this leads to the massive disruption of the nervous system of insects.
o Pyrethroids are much more soluble in fats than in water; they are therefore able to rapidly
reach the target cells within the insects.…read more

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If a greater amount of paraquat is then added, it will be displaced into the soil water,
damaging growing plants.
o Total herbicides are used to clear a large area of land before the crop is planted.
o Selective herbicides are then used to kill the other plants that may be competing with the
desired crop.
o Selective herbicides have been developed which only kill broad-leaved plants, grasses,
grassy weeds etc. The pesticide is selected to suit the type of crop being grown.…read more

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This is related to the other part of the collision theory, which states that the particles must
collide with a certain minimum energy (the activation energy).
o Unless they collide with this minimum amount of energy, they simply bounce off one another
and remain unreacted: this happens to most of the molecules most of the time: at 300K only
1 in 1011 collisions of H2 and N2 is successful.…read more

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The effect of temperature on the rate of the reaction can be seen if the activation energy is
added to the distribution:
o Only those molecules with energy greater than the activation energy are able to react; this is
represented by the areas beneath the graphs to the right of the activation energy line.…read more

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Catalysis
o Catalysts work by providing an alternative reaction pathway for the breaking and remaking
of bonds. The activation energy for this new pathway is often less than the activation energy
of the normal pathway.
o There are two different kinds of catalyst: heterogeneous catalysts are in a different state as
the reactants, and homogenous catalysts are in the same state as the reactants.
o However the catalyst works, its effect is always the same.…read more

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