Rates of reactions

• Particle theory states that all matter is made of particles and are always in constant motion
• Collision theory states that in order for a chemical reaction to take place, two or more reactants must collide with sufficient energy in correct orientation.
• Activation energy is the minimum amount of energy a reactant must have in order to react
• Rate of reaction (RoR) refers to the speed at which a chemical reaction takes place. it is a measure of number of successful collision that occur per unit time.
• To measure RoR you can either measure the change of mass of the reaction mixture or measure the change of volume of gas produced.
• When describing the RoR of a graph, always include:

  1. Shape/gradient of the graph
  2. How much CO2 gas is produced per unit time
  3. Conc. Of reactants and products
  4. Collisions
  5. RoR
• Surface Area


  The number of particles exposed and available to react
• Temperature 


  The average amount of kinetic energy of the particles
• The rate of a chemical reaction can be increased by increasing the surface area exposed of a reactant e.g. chunks into power
• The rate of a chemical reaction can be increased by increasing all or only one of the concentrations of the reactant.
• The rate of a chemical reaction can be increased by increasing the reactant's temperature.
• The higher the temperature the higher kinetic energy. If particles move faster, they are more likely to collide. This increases the frequency of collisions. This means more successful collisions occur, which results in a faster RoR.
• If reactant particles have a higher average kinetic energy, this means a higher proportion of particles have sufficient energy to overcome the activation energy. This means more successful collisions occur, which results in a fast RoR.
• A temperature change in reactants results in:

  • Proportion of successful collisions
  • Frequency of collisions.
• The greater the concentration of the reactant per unit volume, the greater the amount of collisions of the particles will occur per unit of time.
• Increasing the surface area of a reactant increases the rate of reaction as there is more exposed space for the reactants to react.
• Indication of the increase/decrease of the frequency of collisions of reactant particles.