GCSE Chemistry · AQA 8462 · Topic 4.6.1
Rate of reaction
Key points
- Measure rate by following the loss of mass (gas escaping), the volume of gas made (gas syringe), or the time for a solution to turn cloudy (disappearing cross).
- , in units such as g/s or cm³/s. (Higher) Rate in mol/s, and the rate at a moment is the gradient of a tangent to the curve.
- On a graph of product against time, the curve is steepest at the start and levels off when a reactant is used up.
- Collision theory: reactions happen when particles collide with enough energy (the activation energy).
- Increasing concentration or pressure puts more particles in the same space; larger surface area exposes more particles. Both increase the frequency of collisions.
- Raising temperature makes particles move faster, so they collide more often and more collisions have enough energy.
- Catalysts (including enzymes in living things) provide an alternative pathway with a lower activation energy and are not used up.
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The rate of a reaction tells you how quickly reactants are used up or products are formed. You need to calculate rates from data and graphs, and explain the effect of each factor using collision theory.
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