Q.viii. How catalyst increases the rate of reaction? Explain with the help of potential energy diagram for catalyzed and uncatalyzed reactions.

Step 1. A catalyst is a substance that increases reaction rate without being permanently consumed, by opening an alternative reaction pathway.

Step 2. That alternative pathway has a LOWER activation energy, (Ea)2, than the uncatalysed pathway's (Ea)1 -- shown on a potential-energy diagram as two curves that share the same starting (reactant) and ending (product) energy levels but reach different, lower peaks for the catalysed route.

Step 3. Since ΔH is the same net vertical drop for both curves (unchanged by the catalyst), only the height of the barrier changes.

Step 4. Because $f=e^{-E_a/RT}$ responds very sensitively to changes in $E_a$, even a modest reduction in the barrier lets a much larger fraction of colliding molecules qualify as 'successful' at the same temperature -- this is why the observed reaction rate increases in the presence of a catalyst. …

Catalyst lowers Ea via an alternative pathway; PE-diagram comparison; link to the …

• Claiming the catalyst changes ΔH -- it does not; both curves start and end at the same energy levels. …