Which of the following statements about a chemical system in equilibrium is correct/ The

Step 1: Analyze the question We need the one true statement about a chemical system at equilibrium.

Step 2: The concept A chemical equilibrium is dynamic: the forward and backward reactions continue at equal rates, so the concentrations of reactants and products stay constant. Le Chatelier's principle says that when a stress (a change in concentration, pressure, or temperature) is applied to a system at equilibrium, the system shifts to counteract the change and settles into a new equilibrium.

Step 3: Check each option

• A. Reaction is irreversible. False. Equilibrium only exists in reversible reactions.
• B. Reaction goes to completion. False. At equilibrium, reactants and products are both present, so the reaction has not gone to completion.
• C. Equilibrium is re-established when a stress is applied. True. By Le Chatelier's principle, the system shifts and a new equilibrium is established.
• D. Equilibrium position is affected by catalyst. False. A catalyst speeds up both the forward and backward reactions equally. It helps the system reach equilibrium faster but does not change the equilibrium position or the equilibrium constant.

Step 4: Answer The correct option is C.

Exam tip: Remember that a catalyst changes only the rate, never the position. Also, "equilibrium" always means a reversible, dynamic process that does not go to completion. In WASSCE, options with words like "irreversible" or "completion" are almost always wrong for equilibrium questions.