Ammonia Flashcards
raw materials in the haber process
air, methane, steam
how is nitrogen obtained?
Nitrogen is obtained by the fractional distillation of liquid air.
how is hydrogen obtained?
The hydrogen is obtained by the steam reforming of natural gas.
H2O + CH4 → CO + 3H2
CO + 3H2 + H2O → CO2 + 4H2
haber process
The nitrogen and hydrogen are mixed in the ratio 1:3.
This mixture is compressed to a pressure of 200 atm and passed over an iron catalyst at 500oC.
Under these conditions, there is 15% conversion of reactants into ammonia.
The gases leaving the catalysts consist of a small amount of ammonia and large amounts of unreacted nitrogen and hydrogen.
This mixture is passed through a CO system where the ammonia liquidifies and is extracted. The unreacted nitrogen and hydrogen is recycled for further conversion into ammonia.
uses of ammonia
To manufacture fertilisers
To manufacture nitric acid
To manufacture household cleaning agent
To manufacture pharmaceuticals
effect of temperature on haber process
The reaction is exothermic. Hence, the lower the temperature, the greater the yield of ammonia.
N2 + 3H2 ⇌ NH3
In the Haber process, very low temperatures can’t be used since the rate of production will be too slow, i.e. it takes a long time to get a high yield.
A compromise is made between the higher yield for a long time and smaller yields in a shorter time. Hence, the temperature of 500oC is chosen.
effect of pressure on the haber process
the reaction is accompanied by a decrease in volume. Hence, high pressures will increase the yield of ammonia.
A compromise is made between obtaining a high yield of ammonia at high pressures and high cost, and getting a smaller yield at lower pressure and lower cost. Hence, 200 atm is chosen.
why can’t very high pressures be used?
Very high pressures cannot be used since the cost of producing the ammonia will increase.
Stronger equipment
Higher wages
Safety measures
effect of Fe catalyst on the haber process
Catalyst does not increase the yield of ammonia. However, at lower activation energy, such that the yield is obtained in a shorter period.
benefit of using iron catalyst
the iron is porous so it presents a large surface area for gases to react on
effects of ammonia on the environment
eutrophication
smog
human health
soil acidification
changes to plant diversity
changes to plant diversity
Ammonia gas can settle on plant leaves and stems, and cause damage because of its alkalinity in alpine plants.
soil acidifcation
excess ammonium ions in fertilizers are converted to nitrates and hydrogen ions by bacteria
hydrogen ions make soil acidic so plants can’t grow well
effects on human health
Irritates lungs and inhibit uptake of oxygen by haemoglobin by altering pH of blood
Ammonia can react with acids in the atmosphere to form ammonium salts → particulates → can cause bronchitis, asthma and coughing fits when breathed in over time
smog
ammonia contributes with nitrogen and sulphur dioxides fromvehicles and infustry to form fine particles which make smog
eutrophication
Excess quantities of fertilisers pollute rivers and lakes → overgrowth of algae and bacteria → death of aquatic organisms
Rainwater dissolves fertilisers → solution leaches from fields to rivers and lakes → concentration of nitrates and phosphates in the water increases → algae uses the nutrients to grow very fast (algal bloom) → dense growth of algae blocks sunlight → plants and algae die → bacteria feeds on dead plants and algae to multiply rapidly → bacteria uses up oxygen → no oxygen for animals
