Imagine you're on a bicycle at the bottom of a hill. To get to the other side, you have to pedal hard to reach the top first — even if you're going downhill after that! Reactions work the same way. Even exothermic reactions that release energy need a "push" of energy to get started — the activation energy. It's like the energy needed to break apart the reactant molecules before new bonds can form. This is why a match won't spontaneously burst into flame even though combustion releases energy — you need to strike it first to provide that initial activation energy.

🚴 The Hill Climb Analogy

Activation energy is like cycling over a hill! Even if you're going to end up lower (exothermic), you still need to pedal up first. That initial "push" is the activation energy — it gets the reaction started — without this initial push, the molecules cannot rearrange into products. Catalysts are like tunnels through the hill — they give you an easier, lower route to the same destination!

This introduction covers The Energy Hill within Reaction Profiles for GCSE Chemistry. Revise Reaction Profiles in Energy Changes for GCSE Chemistry with 28 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 1 of 13 in this topic. Use this introduction to connect the idea to the wider topic before moving on to questions and flashcards.

Practice questions for Reaction Profiles

What does activation energy represent on a reaction profile?

A. The minimum energy particles need to react
B. The total energy released during the reaction
C. The energy stored in the reactants
D. The difference in energy between products and reactants

1 markfoundation

Explain how a catalyst affects the activation energy shown on a reaction profile. [2 marks]

2 marksstandard

The Energy Hill

Practice questions for Reaction Profiles

Quick recall flashcards

28 questions on Reaction Profiles: practise free