Final answer:
Increasing the pressure in a reaction by decreasing volume causes the equilibrium to shift towards the side with fewer moles of gas, in accordance with Le Chatelier's principle.
Step-by-step explanation:
When the pressure in a reaction is increased by decreasing volume, the reaction initially experiences a higher concentration of gases. According to Le Chatelier's principle, the system will respond to this pressure increase by shifting the equilibrium towards the side with fewer moles of gas. For example, if a reaction has three moles on the reactant side and two moles on the product side, increasing pressure would shift the equilibrium towards the products. This is because the system aims to reduce the pressure by favoring the formation of fewer moles of gas, thus occupying a smaller volume.