Which statement is true about Le Chatelier's Principle?

• A. A catalyst shifts the equilibrium position.
• B. Changing temperature has no effect on equilibrium.
• C. The equilibrium constant is unaffected by changes in temperature.
• D. The system shifts to oppose a change in stress.

Answer: (D)

Le Chatelier's principle describes how a system at equilibrium responds to disturbances: it shifts in a direction that opposes the applied stress, creating a new balance that partially offsets the change. Stress can be changes in concentration, pressure (for gases), or temperature. For example, adding more reactant pushes the equilibrium toward products; removing product shifts toward reactants; increasing pressure on a gas mixture favors the side with fewer moles of gas. A catalyst only speeds up both forward and reverse reactions equally, so it does not change the equilibrium composition. Changing temperature does affect the position of equilibrium and the value of the equilibrium constant, so the statement that temperature has no effect is false. Therefore, the true statement is that the system shifts to oppose a change in stress.