Chemistry Revision: Manufacturing Processes

Nitrogen + Hydrogen=Ammonia REVERSIBLE REACTION

• Nitrogen- Obtained from fractional distillation of liquid air
• Hydrogen- Obtained from reacting methane with steam or from water.

Effect of temperature

• An increase in temperature favours the backward reaction, increasing the speed but reducing the yield
• Reducing the temperature will increase the yield but the time taken will increase
• The temperature used in industry is a compromise 400-500 degrees

Effect of pressure

• Higher pressure will increase the yield as it favours the forward reaction, however this is very expensive. The compromise pressure is 200-250 atmospheres

• Involves the catalytic oxidation of ammonia
• 4NH3 + 5O2 (with a platinum catalyst)=4NO+6H2O

1. Concentrated Ammonia heated gently

2. Stream of Oxygen bubbled through it

3. Coil of platinum wire heated, cooled, then suspended over solution.

4.Wire glows again

5. Can be dangerous as ammonia could burn explosively as side reaction.

Le Chatalier's Principle: If a change is imposed on a system, the system will react to oppose that change.

If a reaction releases energy in a forward direction, it will absorb the same amount of energy in the backward reaction.

If the change in heat energy is positive, the reaction is endothermic, and if it is negative then it is exothermic.

For temperature:

• Exothermic- As temp increases, yield decreases, and viceversa
• Endothermic- As temp decreases, yield increases, " "

For pressure:

• If more gas on the RHS: More pressure means less yield
• If less gas on the RHS: More pressure means more yield