---
title: "How a catalyst increases reaction speed"
subject: "Engineering Chemistry"
chapter: 2
key: "semester_2/engineering_chemistry:catalyst-speed-reaction"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/catalyst-speed-reaction
site: BCT Engineering
---

# How a catalyst increases reaction speed

Engineering Chemistry · Chapter 2: Catalyst

- Asked in: 2070 Magh, 2 marks
- Video: [A Level Chemistry "The Effect of Catalysts on the Rate of Reaction".](https://www.youtube.com/watch?v=PtIWf6pjik0) — Freesciencelessons
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/catalyst-speed-reaction
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-2

## Question

Give an account how a catalyst increases the speed of a reaction.

## Short answer

A catalyst increases reaction speed by providing a new reaction path with lower activation energy. At a given temperature, more molecules have sufficient energy to overcome this lower barrier, so the number of effective collisions and the rate constant increase.

## Answer

A catalyst provides a new reaction path with a **lower activation energy** (Ea). More reacting molecules then have energy equal to or greater than the lowered threshold at the same temperature, so the number of effective collisions rises and the reaction becomes faster (rate constant k = A e^(−Ea/RT) increases). The catalyst is regenerated at the end.

```text
Activation energy on the path R → P

  uncatalysed : ████████████  (high Ea)
  catalysed   : ████          (low Ea)

  Catalyst lowers the barrier; R and P levels unchanged.
```
The energies of reactants (R) and products (P) are unchanged, so ΔH is the same; only the barrier is lowered.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does a catalyst increase reaction speed?
   A. By raising the temperature of reactants
   B. By increasing the energy of products
   C. By providing a new path with lower activation energy
   D. By raising the activation energy
   Answer: C. A lower Ea means more molecules have enough energy, so there are more effective collisions. (Key point: Lower activation energy)

2. According to k = A e^(-Ea/RT), what happens to k when a catalyst lowers Ea at the same T?
   A. k increases
   B. k decreases
   C. k stays the same
   D. k becomes zero
   Answer: A. A smaller Ea makes the exponent less negative, so k and the rate rise. (Key point: Rate constant)

3. What is the effect of a catalyst on DeltaH of a reaction?
   A. DeltaH becomes more negative
   B. None; reactant and product energies are unchanged
   C. DeltaH becomes zero
   D. DeltaH becomes positive
   Answer: B. Only the barrier is lowered; the energies of R and P stay the same. (Key point: Effect on DeltaH)

## Related in Engineering Chemistry

- [Catalyst action; heterogeneous catalysis; adsorption theory](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Acatalyst-heterogeneous-adsorption) — Engineering Chemistry, chapter 2

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