Chemical Reactions 25 25.5 Factors affecting rate of reaction
A range of factors affect the rate at which a chemical reaction takes place. An understanding of the atomic nature of matter and energy changes in chemical reactions allows us to understand why these factors have an effect on rate of reaction.
Particle size Smaller particles react faster. Picture a Rubik’s cube. When it is solid the full outer surface is covered in stickers. However, when the Rubik’s cube is broken up we see more surfaces that were previously hidden inside the Rubik’s cube. These new surfaces do not have stickers. By breaking the Rubik’s cube up into smaller pieces the surface area is increased. During a reaction particles collide with each
other. If these collisions have enough energy (the activation energy) the particles will react and new products will form. However, only the particles at the surface can react. Once the outer particles have reacted and moved away, then the inner particles are on the surface and they can start to collide. When the size of the particles in a reaction are smaller there is more material on the surface available to react and so the reaction is faster.
Fig. 13 The surface area of a Rubik’s cube increases when it is broken up.
Concentration Increasing the concentration of a solution increases the rate of reaction because it means that there are more particles per unit volume of solution to react. When there are more particles, there is a higher number of colliding particles that have the required activation energy for a reaction to take place.
Fig. 14 A concentrated and a dilute solution.
Temperature Increasing the temperature increases the rate of reaction as it gives particles more energy. The more energy the particles have the faster they move and the more collisions there will be between particles that have the required activation energy to react.
Fig. 15 Increasing the temperature increases the rate of reaction.
