In the reaction A + B gives C + D at equilibrium, adding more of substance A will

  • 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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