This topic summary covers Knowledge Organiser: Reaction Profiles 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 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Reaction Profiles
Key Terms
- Reaction profile — energy diagram of a reaction
- Activation energy (Ea) — reactants to peak
- ΔH — reactants to products (overall)
- Peak — the highest-energy point on the profile
- Catalyst — lowers Ea, unchanged at end
Must-Know Facts
- Exothermic: products LOWER than reactants
- Endothermic: products HIGHER than reactants
- Ea = from reactants UP to the peak
- Catalyst: lower peak, same ΔH, same start/end
- Axes: y = Energy, x = Progress of reaction
- Ea is always required — even for exothermic reactions
Key Equations
- ΔH = energy level of products − energy level of reactants
- Exothermic: ΔH negative (products lower on diagram)
- Endothermic: ΔH positive (products higher on diagram)
- Ea = energy from reactant level to peak of profile
Common Mistakes
- Drawing Ea from the peak to the products: Activation energy is measured from the REACTANTS up to the peak — not from the peak down to products
- Saying a catalyst changes ΔH: A catalyst only lowers the activation energy (shorter peak) — the start, end and overall ΔH remain exactly the same
- Forgetting to label axes correctly: y-axis = Energy (kJ/mol); x-axis = Progress of reaction (or Reaction coordinate) — missing labels lose marks
- Drawing exothermic profiles with products higher: In an exothermic reaction, products are at a LOWER energy level than reactants — draw the right side of the curve lower than the left
Practice questions for Reaction Profiles
What does activation energy represent on a reaction profile?
Explain how a catalyst affects the activation energy shown on a reaction profile. [2 marks]
Quick recall flashcards
What is activation energy?
The minimum energy particles need to react when they collide
What does the y-axis show on a reaction profile?
Energy