1.5 Kinetics

• Rate of reaction


  The change of concentration of a reactant or product per unit time
• Rate calculation


  Rate = Amount of reactant used / product made / Time
• For reaction to occur

  1. Particles must collide in the right direction

  2. They must also have a minimum amount of kinetic energy
• Collision theory


  Reactions only take place when collisions occur between particles that have sufficient energy
• Activation energy


  Minimum amount of energy required for a reaction to occur
• When Activation energy is met

  Bonds have sufficient energy to break
• Reactions with lower activation energy


  Need less energy to break bonds, vice versa
• If few particles have energy greater than Ea


  Particles can gain energy through collisions
• Maxwell Boltzmann distribution


  The spread of energies that molecules of a gas have at a particular temperature
• Temperature affects rate of reaction

  Temperature increase results in more particles having energy above Ea, leading to a higher frequency of collisions
• Small increase in Temperature

  Leads to a large increase in rate of reaction
• Pressure affects rate of reaction

  An increase in pressure increases the number of species per unit volume, leading to an increased frequency of collisions
• Concentration affects rate of reaction

  Increasing concentration increases the number of species per unit volume, increasing the frequency of collisions and the rate of reaction
• Catalyst affects rate of reaction

  Adding a catalyst decreases the activation energy, increasing the fraction of successful collisions
• Catalysts


  Do not affect the position of equilibrium but affect the rate at which it reaches, do not affect the yield but only speed up the reaction
• Catalyst


  • Zeolite catalyst
• Surface area affects rate of reaction

  Making a substance into a powder (crushing) increases the surface area available to react, increasing the rate of reaction due to increased collision frequency
• Measuring how long a precipitate takes to form

  Place an arrow on paper and time how long it takes for the cross to disappear (precipitate to form)
• Measuring volume of gas produced

  Measure the amount of gas produced using a syringe over a specific time
• Measuring amount of mass lost

  For reactions that produce a gas, place the reaction on a balance and measure the mass lost as gas is lost
• Use a fume cupboard if gas is harmful or toxic when measuring gas produced
• Explain how increasing concentration affects the rate of reaction: More particles per unit volume, more frequent collisions, rate of reaction increases
• Describe how the Maxwell Boltzmann distribution curve will change when you increase temperature: Total area should remain constant, molecules have a wider range of energies than at lower temperatures, both Emp and mean energy have higher energies