Question

Which of the following will favour the formation of ${\text{N}}{{\text{H}}_3}$ by Haber's process?
A. Increase temperature
B. Increase of pressure
C. Addition of catalyst
D. Addition of promoter with catalyst.

Answer 1

Haber process also known as Haber-Bosch process is the main industrial procedure for the production of ammonia, in which ammonia is synthesised directly from nitrogen and hydrogen. The Haber process combines nitrogen from air with hydrogen derived from natural gas into ammonia.

Complete step by step answer:
In the Haber process the reaction of nitrogen and hydrogen to form ammonia is reversible and exothermic.
The reaction is given below
${{\text{N}}_{2\,\left( g \right)}}\, + \,3{{\text{H}}_{2\,\left( g \right)}}\,\overset {} \leftrightarrows \,\,2\,{\text{N}}{{\text{H}}_{3\,\left( g \right)}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\vartriangle {\text{H}}\,{\text{ = }}\,{\text{ - 92}}\,{\text{KJmo}}{{\text{l}}^{ - 1}}$
Since the reaction is reversible, we need to shift the position of equilibrium as far as possible to the right in order to produce the maximum possible amount of ammonia. Here the forward reaction is exothermic.
According to Le Chatelier's principle, the shift of position of equilibrium to the right will be favoured at lower temperature. As we lower the temperature slower will be the reaction. It is not possible because the gases have to reach equilibrium within a very short time.
When we look at the reaction there are $4$ molecules on the left hand side but only $2$ on the right hand side. According to Le Chatelier's principle, in order to get more ammonia in equilibrium mixture , high pressure is needed. Increasing the pressure will increase the chances of hitting and reaction of the molecules.
Next is addition of catalyst, catalyst has no effect on the position of equilibrium. It only speeds up the reaction. Usually iron is used as catalyst is used in Haber process maintaining the temperature around $400 - 450{\,^{\text{0}}}\,{\text{C}}$ and pressure around $150 - 200\,{\text{atm}}$.
Usually the use of a catalyst such as an iron oxide with small amounts of ${\text{A}}{{\text{l}}_2}{{\text{O}}_3}$ will increase the rate of attainment of equilibrium. Earlier iron is used as a catalyst with molybdenum as a promoter.
So according to Le Chatelier's principle high pressure would favour the formation of ammonia in the Haber process. Also the catalyst along with the promoter will also favour the reaction by speed the reaction to attain the equilibrium.

So, the correct answer is Option B,C,D.

Note: Already said that the addition of a promoter to the catalyst will speed up the reaction , a substance which is not a catalyst by itself , can promote the activity of a catalyst called as promoters. The activity of catalysts can increase by the addition of a small quantity of promoter.