S4 Ammonia Flashcards
What is the volume composition of gases present in dry air?
78% nitrogen
21% oxygen
Remainder: noble gases with argon as main constituent, carbon dioxide
List 2 uses of ammonia.
1) explosives
2) fertilisers
How are the reactants that make ammonia obtained?
Nitrogen extracted from air by fractional distillation of liquid air, and hydrogen is produced from the cracking of petroleum.
What is the effect of temperature on yield of ammonia?
At a lower temperature, the yield of ammonia is higher, and ammonia is less likely to be reduced to hydrogen and nitrogen. However, a lower temperature also results in a slow reaction.
What is the effect of pressure on the yield of ammonia?
At higher pressures, the yield of ammonia is higher. However, maintaining high pressure is costly because of expensive equipment required.
What are the operating conditions of the Haber process?
1) temperature of 450C
2) pressure of 250atm
3) presence of finely divided iron catalyst.
Describe the Haber process. (6)
1) N2 and H2 are mixed in the proportion 1:3
2) the mixture of gases are compressed at the compressor.
3) gases pass over finely divided iron at 450C and 250atm, resulting in an exothermic reaction. It gives out heat and maintains the temperature
4) only 10-15% of nitrogen and hydrogen combine to form ammonia. A mixture of ammonia, nitrogen and hydrogen leaves the converter.
5) the mixture of gases is cooled, and ammonia condenses to form liquid ammonia.
6) unreacted N2 and H2 are pumped back into the converter for further reaction.
Describe the displacement of ammonia from its salts.
When an ammonia salt is heated with an alkali, ammonia is displaced from the salt.
Why should you not add calcium hydroxide to ammonium sulfate, the fertiliser?
When ammonia nitrate is added to calcium hydroxide, they will react to produce ammonia gas and nitrogen will be lost. Plants will be unable to receive nitrogen from ammonia nitrate.
