In the reaction A + B gives C + D at equilibrium, adding more of substance A will
Correct answer: C. shift the equilibrium to the right, forming more C and D
- A. decrease the amount of C formed
- B. have no effect on the position of equilibrium
- C. shift the equilibrium to the right, forming more C and D
- D. change the value of Kc
Explanation
The system responds to the extra A by consuming some of it, which means running the forward reaction further and producing more products until the ratio required by Kc is restored. This is why one reactant is often used in excess industrially when it is the cheaper one. The value of Kc is unchanged, since only temperature can alter it.
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About Le Chatelier's Principle
Le Chatelier's principle predicts how an equilibrium responds when concentration, pressure or temperature changes. Questions apply it to reversible reactions, identify the direction of shift and distinguish genuine equilibrium changes from the effect of a catalyst, which changes the rate of reaching equilibrium but not its position.
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