Final answer:
Increasing the volume of the system for the equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g) shifts the equilibrium towards the reactants due to the increased volume requiring more gas molecules to fill the space, as dictated by Le Chatelier's principle.
Step-by-step explanation:
When the volume of a system containing a gas-phase equilibrium is increased, Le Chatelier's principle tells us that the equilibrium will shift to counteract this change. For the specific equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g), an increase in volume decreases the pressure. Since there are more moles of gas on the reactant side (3 moles) than the product side (2 moles), the equilibrium will shift towards the reactants, thereby increasing the number of moles of gas to 'fill' the increased volume. Similarly, if the volume is decreased, the pressure increases, and the equilibrium shifts to the side with fewer moles of gas, which is the product side in this case, to reduce the pressure.