Rates

• Define rate of reaction.

  the change in the amount of reactant or product in a given time
• units for rate


  mold dm-3 s-1
• What three ways can you measure the rate of reaction other than using concentration changes ?

  1. Use a pH meter to track the acidity overtime
  2. Volume of gas produced - collect with a gas syringe or upturned cylinder
  3. Measure the total mass overtime
  4. Time
• What 5 factors increase the rate of reaction ?

  1. Temperature
  2. Concentration
  3. Pressure
  4. Surface Area
  5. Catalyst
• How does increased temperature affect the rate ?

  Increased temperature increases the kinetic energy of the particles so more frequent and successful collisions happen
• How does increased concentration affect the rate ?

  Increased concentration means more frequent collisions
• How does increased pressure affect the rate ?

  Increased pressure leads to more frequent collisions
• How does a catalyst affect the rate ?

  Increases the rate of reaction as more particles have energy more than the activation energy.
• Describe using collision theory, the effect of increased concentration.

  If the concentration of reactants in solution is increased, then the number of particles in a given volume is higher. As a result, the molecules are now closer together, and so there is a higher chance the molecules are colliding. Collisions will therefore happen more frequently, and so the reaction will proceed at a faster rate.
• Describe using collision theory, the effect of increased pressure.

  If the pressure is increased, the gas molecules are pushed closer together. The same number of molecules now occupy a smaller volume, and so there is an increased chance of the molecules colliding. Collisions will therefore occur more frequently, and so the reaction will proceed at a faster rate.
• Describe using collision theory, the effect of increased temperature.

  Increasing the temperature increases the rate of reaction because at a higher temperature the molecules are moving faster with more energy so there is an increase in collision frequency. At a higher temperature, more molecules have an energy greater than activation energy and so there are more successful collisions.
• Define a catalyst.


  A catalyst increases the rate of reaction, without being used up in the overall reaction, by lowering activation energy
• How does a catalyst work ?


  Catalysts lower the activation energy of a reaction. They do this by providing an alternative route. This results in increased rate.
• What is the difference between a homogeneous catalyst and a heterogeneous catalyst ?

  Homogeneous: when the catalyst and reactants are in the same state

  Heterogeneous: When the catalyst and the reactants are in different states
• Describe using collision theory, the effect of a catalyst.

  A catalyst lowers the activation energy for a reaction by providing an alternative route. There are now more molecules with an energy above than activation energy, so more molecules have enough energy to react, so there are more successful collisions. Hence, catalyst increase the rate of reaction.
• Describe how catalysts increase sustainability by reducing energy consumption.

  • Many industrial processes rely on catalysts. As catalysts speed up the process by lowering activation energy, less energy or lower temperature are required for molecules to react.
  • Much of this energy is supplied by burning fossil fuels e.g. crude oil.
  • Running a process at a lower temperature therefore reduces energy demand.
• Describe how catalysts increase sustainability by helping environmental issues.


  • If less energy is required then less fossil fuels are burnt
  • This means less CO2 gas is released into the atmosphere
  • Catalysts enable a product to be made using different reactions
  • This different method may have fewer products so improving atom economy of the reaction, and so reducing waste