Module 3.2.2- Reaction rates

• Collision theory


  For a reaction to occur, the particles must collide, they must collide with the appropriate orientation, and they must collide with sufficient energy (with the activation energy)
• How does increasing the concentration affect the rate of reaction

  increases the rate of reaction since there are more particles per unit volume and as a result there are more frequent collisions
• How does increasing the pressure affect the rate of reaction

  the concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume. therefore the gas molecules are closer together and collide more frequently
• The progress of a chemical reaction can be followed by:

  monitoring the removal of a reactant

  following the formation of a product
• 2 methods to determine the rate of reaction from the production of gases

  monitoring the volume of gas produced at regular time intervals using gas collection

  monitoring the change in mass using a mass balance
• Catalyst


  substance that speeds up the rate of a chemical reaction without being used up and be regenerated
• How does a catalyst work

  Provides an alternative route with a lower Ea, so more particles have E greater than the Ea , so the proportion of successful collisions increases
• Exothermic enthalpy profile diagram with catalyst

  
• Endothermic enthalpy profile diagram with catalyst

  
• Homogenous catalyst


  a catalyst that is in the same state as all the reactants and products in a reaction system
• Heterogenous catalyst


  a catalyst whose state is different from the reactants'e.g. Haber process, hydrogenation of alkenes
• desorption


  Release of an adsorbed (weakly bonded) substance from a surface.occurs on heterogenous catalysts
• Catalysis- sustainability and economic importance

  less energy required therefore less electricity and fossil fuel

  making products faster with less energy cuts costs and increases profitability
• Boltzmann distribution


  The distribution of energies of molecules at a particular temperature, usually shown as a graph.

  no molecules have 0 energy

  area under the graph = total number of molecules

  no maximum energy for a molecule

  
• Increasing temperature on a Boltzmann distribution graph

  more molecules have energy greater than or equal to the activation energy

  greater proportion of collisions

  rate of reaction increases due to more frequent successful collisions

  
• Adding a catalyst on a Boltzmann distribution graph

  a greater proportion of molecules have energy greater than or equal to the activation energy

  greater proportion of collisions

  rate of reaction increases due to more frequent successful collisions