This definitions covers Key Definitions 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 8 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
Reaction profile (energy level diagram): A diagram showing how the energy of reacting particles changes during a reaction, from reactants through the peak to products.
Activation energy (Ea): The minimum energy that colliding particles must have to react. Measured as the height from the reactants energy level to the peak of the profile.
Catalyst: A substance that speeds up a reaction by providing an alternative reaction pathway with a lower activation energy. It is not used up and remains chemically unchanged at the end.
ΔH (enthalpy (energy change)): The difference in energy between the products and reactants. Negative ΔH = exothermic; positive ΔH = endothermic. Measured from reactants to products on the profile.
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]