Quick questions on Speed of reaction and collision theory explained: O-Level Chemistry

For a reaction to happen, particles must collide with one another, and the collision must be successful: the particles must collide with at least a minimum energy, the activation energy, and in the right orientation. Not every collision leads to a reaction; only the energetic, well-aimed ones do. Anything that increases the frequency of collisions, or the proportion that have enough energy, speeds the reaction up.

Increasing the concentration of a solution puts more reactant particles in the same volume. The particles are closer together, so they collide more often. More frequent collisions mean more successful collisions per second, so the rate increases. Diluting the solution has the opposite effect.

Increasing the pressure of a gas squeezes the same number of particles into a smaller volume, so they are closer together and collide more often. As with concentration, more frequent collisions increase the rate. Pressure has this effect only for reactions involving gases.

Breaking a solid into smaller pieces (or using a powder) increases its surface area. More of the solid is exposed to the other reactant, so there are more frequent collisions at the surface, and the rate increases. This is why powdered solids react faster than large lumps.

Increasing the temperature gives the particles more kinetic energy, so they move faster. This has two effects:

State two factors that increase the rate of a reaction. [1 mark]

Explain, using collision theory, why increasing the concentration of a solution increases the rate. [2 marks]

Explain why a reaction speeds up when the temperature is raised. [3 marks]