Ammonia Flashcards
What is chemical equation for the formation of NH3?
N2 (g) +3 H2 (g) <=> 2 NH3 (g)
How is N2 obtained?
Nitrogen is obtained by fractional distillation of liquified air
How is H2 obtained?
Hydrogen is obtained by cracking of crude oil/petroleum
What are the conditions needed for the Haber process?
450°C
200 atm
Finely divided iron catalyst
Why is 200 atm used?
Higher pressure produces even more ammonia but it is more expensive to build pipes to withstand high pressure and is also dangerous/ high risk of explosion
Why is 450°C used?
Lower temperature will have a higher yield but slower rate of reaction,
What is a reversible reaction?
A reaction that can go both forwards and backwards at the same time.
(to form products or form back reactants at the same time)
Define Dynamic equilibrium and key conditions necessary
DE is the state where rate of forward and backward reaction is the same.
There is no observable change
Reaction does not stop, but no net change in concentration of products
In order to achieve DE, Reaction must:
- Be reversible
- In a closed system
Describe the Haber process
- N2 and H2 is mixed in proportion in 1: ratio
- Mixture of gases is compressed to 200 atm
- Gases are heated to 450°C and passed over finely divided iron catalyst
- reaction is exothermic
- Only 10% - 15% of N2 & H2 is converted to ammonia - Mixture of ammonia, nitrogen & hydrogen is obtained, mixture is cooled
- Ammonia gas condenses to form liquid ammonia
- Unreacted nitrogen & hydrogen are pumped back into the converter (recycled) for further reaction
Why do farmers avoid using calcium hydroxide(slaked lime) or nitrogenous fertilisers?
Ca(OH)2 will react with ammonia to produce calcium nitrate, H2O and NH3,
Nitrogen, important for plane growth, will escape into the air in the form of ammonia, making both fertiliser & calcium hydroxide ineffective
