The Rate and Extent of Chemical Change

This unit covers rates of reaction, the factors affecting them, collision theory, catalysts, and reversible reactions and equilibrium including Le Chatelier's principle at Higher tier.

Collision theory is the explanation behind every rate question, so learn it properly: reactions happen when particles collide with sufficient energy, and anything that increases the frequency or energy of collisions increases the rate. Answers that describe particles moving faster without linking to collisions earn less. Rate graphs are examined regularly, and the ability to describe why a curve levels off, or to draw a tangent to find rate at a point, is worth practising. Equilibrium questions reward applying Le Chatelier systematically rather than by instinct. One required practical on rates sits here and is examined directly.