How It Works: Reading and Drawing Reaction Profiles
Part of Reaction Profiles — GCSE Chemistry
This how it works covers How It Works: Reading and Drawing 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 4 of 13 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 13
Practice
28 questions
Recall
15 flashcards
⚙️ How It Works: Reading and Drawing Reaction Profiles
A reaction profile (also called an energy level diagram) is a graph that shows how the energy of the reacting particles changes as they go from reactants to products. The y-axis shows the energy (in kJ/mol), and the x-axis shows the "progress of the reaction" (sometimes called the reaction coordinate).
The diagram has three key features: (1) the energy level of the REACTANTS (the flat line on the left), (2) the PEAK of the curve (representing the transition state — the point of maximum energy where old bonds are breaking and new bonds are starting to form), and (3) the energy level of the PRODUCTS (the flat line on the right).
The ACTIVATION ENERGY (Ea) is measured as the vertical distance from the reactants energy level up to the peak. This is the minimum energy that colliding particles must have in order for the reaction to proceed. A higher peak means a higher activation energy and a slower reaction at a given temperature.
The overall energy change (ΔH) is measured as the vertical distance between the reactant energy level and the product energy level. If products are lower → exothermic (ΔH negative). If products are higher → endothermic (ΔH positive). Importantly, ΔH is NOT measured from the peak — it is measured from reactants to products.