Final answer:
The position of equilibrium is affected by changes in pressure when gas molecules are involved and when there's a change in the number of moles of gases on either side of the reaction. Le Chatelier's principle dictates that an increase in pressure will shift the equilibrium towards the side with fewer gas molecules. Adding inert gases at constant volume does not affect the equilibrium as partial pressures remain unchanged.
Step-by-step explanation:
When we discuss the effect of pressure on a system at equilibrium, it's crucial to focus on chemical reactions that involve gases. Altering the pressure of a system can change the position of equilibrium if there's a difference in the number of moles of gases between the reactants and products. According to Le Chatelier's principle, the system responds to the change in pressure by shifting the equilibrium position to counteract the pressure increase. For instance, increasing the pressure of a reaction that produces fewer gas molecules will shift the equilibrium toward the side with fewer gas molecules to lower the pressure.
However, if you add an inert gas to the system at constant volume, there's no effect on the equilibrium position because it does not change the partial pressures of the reacting gases. In a nutshell, pressure changes significantly disturb the equilibrium only in gas reactions with unequal moles on either side of the reaction equation. Systems that do not involve gases, or have an equal number of moles of gas on both sides, are generally not affected by pressure changes.