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?

  1. Reactants bind to the catalyst’s surface, forming an intermediate complex.

  2. The complex rearranges, breaking old bonds and forming new ones with less energy required.

  3. 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 TypeActivation Energy (\$E_a\$)With Catalyst
UncatalysedHigh—
CatalysedLowSame 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.