State that a catalyst decreases the activation energy, $E_a$, of a reaction
Chemical Reactions – Rate of Reaction
What is a Catalyst?
A catalyst is like a friendly guide that helps a reaction happen faster, but it never gets used up. Imagine you’re walking through a maze. A catalyst is a hidden shortcut that lets you reach the exit quicker without changing the maze itself. 🚶♂️➡️🏁
In chemical terms, a catalyst lowers the activation energy ($E_a$) – the energy barrier that reactants must overcome to form products. Because the barrier is lower, more molecules have enough energy at a given temperature, so the reaction rate increases. 🔬
How Does a Catalyst Work?
- Reactants bind to the catalyst’s surface, forming an intermediate complex.
- The complex rearranges, breaking old bonds and forming new ones with less energy required.
- Products are released, and the catalyst is free to start another cycle.
Exam Tip 💡
• Remember: catalysts lower $E_a$ but do not change the overall ΔG of the reaction. • In multiple‑choice questions, look for statements that say “decreases the activation energy” or “provides an alternative pathway with lower energy.” • For short answer, explain that a catalyst offers a lower‑energy route, increasing the number of successful collisions per unit time.
Illustration: Activation Energy Barriers
| Reaction Type | Activation Energy ($E_a$) | With Catalyst |
|---|---|---|
| Uncatalysed | High | — |
| Catalysed | Low | Same as uncatalysed (overall ΔG unchanged) |
Quick Recap 📚
- A catalyst lowers the activation energy ($E_a$).
- It provides an alternative reaction pathway with a lower energy barrier.
- Reaction rate increases, but the catalyst itself is unchanged after the reaction.
- Use the phrase “decreases $E_a$” when answering exam questions.
Revision
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