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.
ÎH (enthalpy (energy change)): The difference in energy between the products and reactants. Negative ÎH = exothermic; positive ÎH = endothermic. Measured from reactants to products on the profile.
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.
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]