A CATALYST is added to a system at equilibrium. Which of the following effects does the catalyst have?
AIt increases the equilibrium constant $K_c$
BIt decreases the equilibrium constant $K_c$
CIt does NOT change $K_c$; it speeds both directions equally
DIt shifts the equilibrium toward the products
Answer & Solution
Correct answer: C. It does NOT change $K_c$; it speeds both directions equally
1. A catalyst provides an alternative pathway with a lower activation energy.
2. Because the SAME alternative pathway is offered to both forward and reverse reactions, the rates of BOTH increase by the same factor.
3. The equilibrium constant $K_c = k_f / k_r$ (ratio of forward to reverse rate constants) is therefore UNCHANGED.
4. The catalyst only changes HOW FAST equilibrium is reached, not WHERE it lies.
5. Options A, B, and D would shift the equilibrium itself, which a catalyst cannot do.
_Source: NCERT Class 11 Chemistry, Ch 6, §6.8.3 (Effect of a Catalyst on equilibrium), p. 21._
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