Ammonia

Preparation

Haber’s Process

Commercial production of ammonia is done by Haber’s Process. $$ ce{N2(g) + 3H2(g) <=> 2NH3(g) ; $Delta _fH^{Theta}$ = – 46.1 $ kJ -mol^{–1}$ }$$

The reaction is reversible and exothermic. Total number of particles produced are less than the reacting particles. Thus, as per Le Chatelier’s Principle , low temperature and high pressure will drive the reaction to the right. But at low temperature, the rate of reaction in reaching equilibrium is too slow to be of economical value and it requires catalysts. Practically, temperature is increased to achieve equilibrium faster. Though it lessens percentage of conversion of nitrogen and hydrogen into ammonia, but faster rate of conversion make it economical. The optimum conditions for this conversion is a temperature of 700 K and a pressure of 200 atm (about 20 MPa) and the use of catalyst such as iron oxides with small amount of (ce{Al2O3}) and (ce{K2O}). (Iron promoted with molybdenum is also used as catalyst for the same purpose). The attached diagram shows the flow of Haber’s Process.

First, nitrogen and hydrogen is fed and compressed to the pressure of 20 MPa. Then, the mixture is passed through container containing the catalyst and maintained at 700 K. The gas mixture after the reaction is allowed to cool down. It condenses ammonia into liquid. The residual gases of nitrogen and hydrogen are recycled.

The reaction is also called as Haber-Bosch Process.

Structure and Physical Properties

Chemical Properties

(ce{})