Haber Process is given by the following reaction:
$N_{2}(g)+3H_{2}(g)\rightleftharpoons2NH_{3}(g)$
When pressure in the process is increased then reaction will shift in direction:

Question

Haber Process is given by the following reaction: 
$N_{2}(g)+3H_{2}(g)\rightleftharpoons2NH_{3}(g)$ 
When pressure in the process is increased then reaction will shift in direction:

Accepted Answer

The correct option is (1):
To understand why the reaction shifts in the forward direction when pressure is increased, we need to apply Le Chatelier's Principle. Le Chatelier's Principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. In this case, the stress is an increase in pressure.

For gaseous reactions, an increase in pressure favors the side of the reaction with fewer moles of gas. Let's look at the given Haber process reaction:
$N\_{2}(g)+3H\_{2}(g)\rightleftharpoons2NH\_{3}(g)$

On the reactant side ($N\_{2}(g)+3H\_{2}(g)$), there is $1$ mole of $N\_{2}$ and $3$ moles of $H\_{2}$, totaling $1+3=4$ moles of gas.
On the product side ($2NH\_{3}(g)$), there are $2$ moles of $NH\_{3}$ gas.

Comparing the moles of gas on both sides:
Reactant side: $4$ moles of gas
Product side: $2$ moles of gas

Since the product side has fewer moles of gas ($2 < 4$), an increase in pressure will shift the equilibrium towards the product side to reduce the total number of gaseous molecules, thereby relieving the pressure stress. This means the reaction will shift in the forward direction, favoring the formation of ammonia ($NH_{3}$). This is a key principle utilized in industrial ammonia production to maximize yield.

The incorrect option is (2): If the reaction were to shift backward, it would lead to an increase in the number of gas moles (from 2 moles to 4 moles), which would further increase the pressure, contrary to Le Chatelier's principle.
The incorrect option is (3): The system is under stress due to the increased pressure, and according to Le Chatelier's principle, the equilibrium must shift to relieve this stress. Therefore, it cannot remain unchanged.
The incorrect option is (4): The shift in equilibrium in response to a change in pressure is a single, direct response dictated by the number of gas moles on each side of the reaction, not a sequential shift first in one direction and then another.