C6.1.2 Haber Process

Question 1

Haber process

Answer 1

Important industrial process. Produces ammonia (NH3) make fertilisers
Haber process used to make ammonia from hydrogen + nitrogen:
NITROGEN + HYDROGEN ——> AMMONIA (forward + backward)
N2 (g) + 3H2 (g) ——> 2NH3(g) (forward + backward)

Question 2

Industrial conditions

Answer 2

Pressure= 200 atmospheres 
Temperature = 450
Catalyst = iron

Question 3

How it works

Answer 3

Reaction is well suited for an industrial scale as the reactants aren’t too difficult/expensive to obtain

1) nitrogen obtained easily from air = 78% nitrogen
2) hydrogen mainly comes from reacting methane (from natural gas) w steam —> H2 + CO2
3) reactant gases passed over an iron catalyst. High temp (450) + high pressure (200 atmospheres)
4) reaction is reversible some ammonia produced converts back into H2 + N2. Eventually reaches dynamic equilibrium
5) ammonia formed as a gas but as it cools in the condenser = liquefies + is removed. Unused H2 + N2 are recycled so nothing is wasted
6) ammonia produced can then be used to make ammonium nitrate = nitrogen-rich fertiliser

Question 4

Why is it important?

Answer 4

Without the Haber process we wouldn’t have fertilisers which has allowed human pop to grow quickly as it has over last 100 yrs.

Question 5

Reaction is reversible so…

Answer 5

… a compromise has to be made
Temp + pressure affect rate of reaction
These factors affect position of equilibrium for a reversible reaction

Question 6

Factors that affect

Answer 6

1) forward reaction is exo. Means that increasing the temp will move equilibrium away from ammonia towards N2+h2. So yield greater at lower temps
2) lower temp = lower rate of reaction (equilibrium reached slower)
3) 450 is a compromise between max yield + speed of reaction. Better to wait 20 seconds for 10% yield have to wait 60 seconds for 20% yield
4) higher pressure moves equilibrium towards products there are 4 molecules of gas on left side for every two molecules on right. Increasing pressure maximises percentage yield + increases ror
5) pressure is set as high as possible without making process too expensive/dangerous to build + maintain. So 200 atmospheres operating pressure
6) iron catalyst makes reaction to faster but doesn’t affect yield