Le Chatelier's principle predicts that increasing pressure in a reaction system with gases will shift toward the side with fewer moles of gas.

• A. True
• B. False
• C. It depends on temperature
• D. Only for catalysts

Answer: (A)

Le Chatelier's principle says that a system at equilibrium will adjust to counteract a disturbance. When the disturbance is an increase in pressure for a mixture of gases, the system lowers the pressure by shifting the equilibrium toward the side that has fewer gas molecules. In other words, the direction of the shift is determined by the difference in the number of moles of gas on each side: if the product side has fewer gas molecules, the equilibrium moves toward products; if the reactant side has fewer, it moves toward reactants. Catalysts only speed up how fast equilibrium is reached and do not change its position, and changing temperature affects the equilibrium constant rather than the immediate pressure-driven shift at a fixed temperature. So increasing pressure in a gas-phase system tends to favor the side with fewer moles of gas, making the statement true.