Unit 2.2

• Rate = change in concentration ÷ time
• The larger the surface area, the more molecules exposed to the reactants, therefore more successful collisions and the faster the rate of reaction.
• The higher the concentration, the more particles there are in a given volume, increasing the number of successful collisions and increasing the rate.
• The higher the temperature, the more kinetic energy particles have. This means that more particles have sufficient energy to react (activation energy) so there are more successful collisions (faster rate).
• A catalyst provides an alternative reaction pathway that has a lower activation energy, so more particles have sufficient energy to react (more successful collsions) and therefore increases the rate.
• Chemical reactions occur when particles collude. However, not all collisions result in a chemical reaction. For a collision to be successful, the particles have to collide at the correct orientations and with enough energy (activation energy).
• Activation energy is the minimum energy required for a reaction to occur
• A homogenous catalyst is in the same state as the reactants.
• A heterogenous catalyst is in a different state to the reactants.
• Some reaction mixture can show a steady change of colour as the reaction proceeds. The concentration of the substance changing colour can be monitored using a colourimeter. The colourimeter selects a filter of the same colour of light which the sample absorbs. The filtered light shines through the sample to a detector (a photocell) which detects the intensity of the light.