This exam tips covers Exam Tips for 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 12 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips for Reaction Profiles
🎯 Common Question Types:
- "Draw a reaction profile for an exothermic/endothermic reaction" (3 marks)
- "Add the curve showing the effect of a catalyst" (2 marks)
- "Using the diagram, calculate the activation energy" (1-2 marks)
- "Explain how a catalyst increases the rate of reaction" (3 marks)
📝 Key Command Words:
- Label correctly: y-axis = Energy, x-axis = Progress of reaction
- Ea is measured from reactants to peak, not from the x-axis
- ΔH is the difference between reactant and product energy levels
⚠️ Common Mistakes to Avoid:
- Drawing the catalyst curve with a different start/end point — same reactants and products always!
- Saying catalysts "give" energy — they provide an alternative pathway with lower Ea
- Measuring Ea from the x-axis — always measure from the reactants level
- Forgetting to label the axes — these are easy marks to lose
Quick Check: Explain why even exothermic reactions need activation energy to start.
Before new bonds can form in the products, the existing bonds in the reactant molecules must first be broken. Breaking bonds always requires an input of energy. This energy needed to start the bond-breaking process is the activation energy. Even though the overall reaction releases energy (exothermic), there is still an energy "barrier" to overcome first — the reaction cannot just happen spontaneously without this initial push.
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]