Haber Process - Industrial Process of Ammonia

What is the haber process?

Nitrogen + Hydrogen reversible reaction to ammonia
N2 + 3H2 ⇌ 2NH3

What is this symbol ⇌

Double arrow, reversible reaction

What is a reversible reaction?

A reaction where both the forward + reverse reactions can occur

What is equillibrium?

Forward + reverse reactions occur at the same rate, as quick as something’s broken down, it’s being formed.

What are the raw materials in the haber process?

• Nitrogen is taken from the air by fractional distillation of liquid air.

  • Hydrogen is obtained from methane by reacting it with steam (CH4 + H2O ——> 3H2 + CO)

What are the reaction conditions of the haber process

1. Nitrogen and Hydrogen are piped into the reaction system

2. Pressure of gases increased to 200atm

3. Gases are heated at 450 degrees + passed over an iron catalyst

4. The equilibrium mixture is cooled, condensing out NH3

5. Unreacted Nitrogen and Hydrogen are recycled

450 degrees celcius

200 atm

Iron catalyst

What is le chatelier’s principle?

A system at equilibrium will shift the position of equilibrium to oppose a change imposed upon the system. If a forward reaction is exothermic, the backwards reaction is endothermic + vice versa

What’s an exothermic reaction

Reaction releasing energy

What’s an endothermic reaction

Reaction absorbing energy

How is le chatelier’s principle used in the haber process?

High pressure favours sides with fewer moles of gas therefore the yield of ammonia is increased. The side of nitrogen and hydrogen have more pressure because they have 4 molecules compared the ammonias 2 molecules. But too high a pressure is expensive (  needs thicker, stronger pipes for safety)

What is the forward reaction of the haber process?

Forwards reaction is exothermic

Low temperatures favour exothermic reaction, increasing yield of ammonia and vice versa

Too low a temperature has a slow rate of reaction (compromise of 450 degrees celcius)

What are the uses of ammonia?

Fertilisers + Explosives

Structure and bonding of ammonia

• Simple molecular structure

• Covalent bonds

Temperature of 450 degree compromise between reaction rate, equilibrium yield and cost

• A high temperature decreases the equilibrium yield because the forward reaction is exothermic, in order to oppose this, the reaction is shifted in the endothermic direction.

• At a high temperature, the reaction rate increases because there is more energy for particles to speed up + collide more frequently.

• But a high temperature needs more energy which is more costly

Pressure of 200 atm compromise between reaction rate, equilibrium yield + cost

• A high pressure increases the equilibrium yield because the forward reaction has less moles. An increase in pressure pushes equilibrium towards ammonia

• At a high pressure, the reaction rate increases because the particles are closer together, increasing collision frequency

• But too high a pressure requires thicker pipes, more costly, and too high a pressure risks an explosion

Use of catalyst (iron) in reaction rate, equilibrium yield + cost

• The use of iron as a catalyst increases the rate of forward + backward reaction because reaction reaches equilibrium quicker, so the yield is decreased

• The reaction rate will increase because it provides an alternate pathway with less activation energy.

• It can reduce the costs because it allows for a lower temperature therefore less energy needs to be used, less costly.

What happens to the unreacted nitrogen + hydrogen?

The N2 + H2 are recycled to make more ammonia

How is the ammonia removed from the reaction mixture?

The reaction mixture is cooled to liquify the ammonia