Contact And Haber Process Flashcards
What is the first step of the contact process?
Make sulphur dioxide by brining sulphur in excess of air
S(s) + O2(g) ⇒ SO2(g)
What is the second step of the contact process?
Convert sulphur dioxide to sulphur trioxide
2SO2 + O2⇌ 2SO3 ΔH = -ve
Why do you use a catalyst? (Contact process)
Use Venadium(V) oxide to speed up reaction
What and why is the temperature? (Contact process)
450ºC
Forward sreaction is exo ∴ low temp favours forward reaction ∴ high yield
BUT too low temp = low RoR ∴ need to compromise
What and why is the pressure? (Contact process)
• up to 2 atms
Lord side has fewer molecules than reactant side ∴ incr pressure favours forward reaction ∴ high yield.
Also, higher pressure increases RoR
What happens at stage three of the contact process?
Sulphur trioxide reacts w sulfuric acid to form oleum
SO3(g) +H2SO4(aq) ⇒ H2S2Oy(aq)
Why can’t sulfur trioxide react straight w water?
- not safe- produces steamy fumes of sulfuric acid
* low yield
What is stage 4 of the contact process?
Oleum reacts w water to form sulfuric acid
H2S2O7(aq) + H2O(l) ⇒ 2H2SO4(aq)
What is sulfuric acid used for?
Paints, dyes, detergents, soaps, fertilisers w methane
What do you need for the haber process and where do you get it from?
- nitrogen ➯ fractional distillation of air
* hydrogen ➯ from methane and water (CH4 + 2H2O ⇒ CO2 + 4H2), or cracking hydrocarbons
What is the haber process equation?
nitrogen + hydrogen ⇌ ammonia (reversible reaction) ΔH -ve
N2 + 3H2 ⇒ 2NH3
What temp is the haber process at and why?
450ºC.
Low temp is better as system opposes change to favour forward reaction, as that is exo, ∴ high yield as eq shifts to right
However at low temp, RoR is slow ∴ compromise is 450ºC
What pressure is the haber process at and why?
200-300 atms
Good to have high pressure because favours forward reaction as has 2 molecules not 4 ∴ high yield
But, high pressure is expensive as must pay for strong container/pipes and higher power costs for compressor. Also danger of explosion/injury ∴ compro = 200-300atms
What catalyst is used in the haber process and why?
Iron
Faster RoR and lower operating temperatures
What happens after the haber process reaction?
Mixture of gases cooled down, ammonia first to liquefy ∴ separated
Leftover N2 and h2 recycled and used again
Low yield, roughly 28%
