Le Chatelier's principle states that when a change is made to a system at equilibrium, the system will shift in the direction that opposes the change. In other words, the system will try to counteract the change and restore equilibrium.

For a gaseous system at equilibrium, a change in pressure will cause the system to shift in the direction that opposes the change in pressure. If the pressure is increased, the system will shift in the direction that decreases the pressure. If the pressure is decreased, the system will shift in the direction that increases the pressure.

For example, consider a gaseous system at equilibrium that contains nitrogen and hydrogen gases. If the pressure of the system is increased, the system will shift in the direction that decreases the pressure. This means that the reaction will shift towards the side with fewer moles of gas, which is the side with only nitrogen gas.

Conversely, if the pressure of the system is decreased, the system will shift in the direction that increases the pressure. This means that the reaction will shift towards the side with more moles of gas, which is the side with both nitrogen and hydrogen gases.

In general, the effect of a change in pressure on a gaseous system equilibrium can be predicted using Le Chatelier's principle. The system will shift in the direction that opposes the change in pressure.