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Topic 7: Rates of reaction and energy changes

4 dot points across 4 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do we calculate the overall energy change of a reaction from bond energies?

Bond energy calculations: breaking bonds is endothermic and making bonds is exothermic, and calculating the overall energy change of a reaction from bond energies.
A focused answer to Edexcel GCSE Chemistry topic 7, covering why bond breaking is endothermic and bond making is exothermic, and how to calculate the overall energy change of a reaction from bond energies as the energy to break bonds minus the energy released making bonds, including identifying exothermic and endothermic reactions from the result.
9 min answer →

What is the difference between exothermic and endothermic reactions, and how do reaction profiles show it?

Exothermic and endothermic reactions: the energy transfer to or from the surroundings, examples and temperature changes, reaction profiles and activation energy, and the core practical on temperature change.
A focused answer to Edexcel GCSE Chemistry topic 7, covering the difference between exothermic and endothermic reactions, examples and the temperature changes they cause, how reaction profiles show the energy change and the activation energy, and the core practical investigating temperature changes in reactions.
9 min answer →

How do we measure the rate of a reaction, and how do catalysts speed reactions up?

Measuring rates and catalysts: the core practicals measuring rate by gas volume and by a colour change, calculating rate from a graph, and how catalysts work by lowering the activation energy.
A focused answer to Edexcel GCSE Chemistry topic 7, covering the core practicals that measure the rate of reaction by the volume of gas produced and by the time for a precipitate to obscure a cross, how to calculate rate from a graph including the gradient of a tangent, and how catalysts increase rate by providing a pathway with a lower activation energy.
10 min answer →

What is the rate of a reaction, and how does collision theory explain the factors that change it?

Rates of reaction and collision theory: the meaning of rate, how concentration, pressure, surface area and temperature affect rate, and the explanation in terms of collision frequency and activation energy.
A focused answer to Edexcel GCSE Chemistry topic 7, covering what the rate of a reaction means, collision theory and activation energy, and how concentration, pressure, surface area and temperature change the rate by altering the frequency and energy of collisions.
9 min answer →