Q.xvi. Explain graphically the effect of catalyst on the rate of reaction.

Step 1. Potential-energy-diagram view. Two curves are plotted on the same reactants-to-products energy profile: the uncatalysed curve rises to a higher peak, barrier height (Ea)1; the catalysed curve, via its alternative pathway, rises to a visibly lower peak, barrier height (Ea)2 < (Ea)1. Both curves start and end at the same energy levels (ΔH unchanged).

Step 2. Energy-distribution view. A single fraction-of-molecules-vs-energy curve is drawn with two threshold lines marked: the higher uncatalysed Ea and the lower catalysed Ea. The shaded area beyond the LOWER (catalysed) threshold is visibly larger than the area beyond the higher (uncatalysed) threshold. …

Two complementary graphical devices (PE-barrier diagram; energy-distribution-with-threshold d …

• Drawing the catalysed and uncatalysed PE curves with DIFFERENT starting/ending energy levels -- a catalyst must not change the reactants' or products' own energies, only the barrier height between them. …