When Δn (the change in the number of moles of gas) is greater than 1, the effect of pressure on an equilibrium reaction can be explained using Le Chatelier's principle. This principle states that if a system at equilibrium is subjected to a change, it will respond in a way that minimizes the effect of that change.

Explanation:

1. Le Chatelier's Principle:
Le Chatelier's principle helps us understand how changes in pressure can affect the equilibrium of a reaction. According to this principle, if the pressure on a system at equilibrium is increased, the system will shift in the direction that reduces the total number of moles of gas. On the other hand, if the pressure is decreased, the system will shift in the direction that increases the total number of moles of gas.

2. Effect of Pressure:
When Δn is greater than 1, it implies that the total number of moles of gas on the product side is greater than the total number of moles on the reactant side. In this case, the reaction is said to have a positive change in molar volume.

When the pressure is increased:

- The system will shift in the direction that reduces the total number of moles of gas to relieve the pressure.
- If the reactants have a lower total number of moles of gas, the equilibrium will shift towards the reactant side.
- If the products have a lower total number of moles of gas, the equilibrium will shift towards the product side.

When the pressure is decreased:

- The system will shift in the direction that increases the total number of moles of gas to compensate for the decreased pressure.
- If the reactants have a higher total number of moles of gas, the equilibrium will shift towards the product side.
- If the products have a higher total number of moles of gas, the equilibrium will shift towards the reactant side.

3. Example:
Consider the reaction:
N2(g) + 3H2(g) ⇌ 2NH3(g)

In this reaction, Δn = (2 moles of gas on the product side) - (4 moles of gas on the reactant side) = -2.

When the pressure is increased, the equilibrium will shift towards the side with fewer moles of gas, which is the reactant side. This will result in the formation of more N2 and H2 and less NH3.

When the pressure is decreased, the equilibrium will shift towards the side with more moles of gas, which is the product side. This will result in the formation of more NH3 and less N2 and H2.

Conclusion:
When Δn is greater than 1, changes in pressure can affect the equilibrium of a reaction. By applying Le Chatelier's principle, we can predict the direction in which the equilibrium will shift in response to changes in pressure.