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 reaction".
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 (the maximum energy point — this is the activation energy barrier that reacting particles must overcome), 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, because fewer particles have energy greater than or equal to the activation energy.
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.
In an endothermic reaction, the products end up at a higher energy level than the reactants. That extra energy must come from somewhere — it comes from the thermal energy of the surroundings. The surroundings cool down because their heat energy has been transferred into the reacting mixture. This is why dissolving ammonium nitrate in water makes the beaker feel cold to the touch.