Central question: Why does a catalyst have no effect on equilibrium position or K?

Chain 1: Activation Energy Argument

Catalyst provides an alternate pathway with lower activation energy → Ea for forward reaction decreases → rate constant kf increases → BUT catalyst lowers Ea for backward reaction by the SAME AMOUNT → kb increases by same factor → ratio kf/kb (= K) remains unchanged → equilibrium position unchanged.

Chain 2: Thermodynamic Argument

K depends on $\Delta G$° = −RT ln K → $\Delta G$° depends only on the intrinsic thermodynamic stability of reactants and products → a catalyst does not change the energy of reactants or products → $\Delta G$° unchanged → K unchanged → equilibrium position unchanged.

Chain 3: Time vs Position Argument

A catalyst speeds up the APPROACH to equilibrium (time to reach equilibrium decreases) → it does NOT change WHERE equilibrium lies (position and K are the same) → in a NEET question: catalyst "increases rate of attainment of equilibrium" is correct; "shifts equilibrium" is WRONG.

Chain 4: Practical Analogy

Think of equilibrium as a balance scale: two pans held by a pivot. A catalyst is like oiling the pivot — the scale tips faster to its natural resting point, but the natural resting point (K) is determined by the weights (thermodynamics), not the oil (catalyst).

Conclusion: Catalyst faster attainment → NO shift → NO change in K → NO change in concentrations at equilibrium