• The collision theory states that particles collide with enough energy and with the correct orientation to break the bonds between them.
• This is associated with activation energy which is the minimum amount of energy needed for successful collisions to occur.

Do you remember what factors affect the rate of reaction in AS/A-level Chemistry?

• Increased surface area:
  Increased particles at surface meaning that there are more collisions, which allows for more successful collisions, thus increasing the rate of reaction.
   
• Increased temperature:
  The particles move faster with more kinetic energy meaning that they collide more frequently which allows for more successful collisions and an increased rate of reaction.
   
• Increased concentration (solutions):
  There are more particles which means that there are more collisions occurring allowing for more successful collisions and an increased rate of reaction. However, as the reactants are used up the concentration gradient falls meaning the rate of reaction will drop.
   
• Increased pressure (gases):
  There are more particles which means that there are more collisions occurring allowing for more successful collisions and an increased rate of reaction.
   
• Decreased volume:
  There is the same no. of particles but a smaller area meaning that there are more collisions allowing for more successful collisions and an increased rate of reaction.
   
• Using a catalyst:
  These are substances that will increase the rate of chemical reactions without being chemically changed.

• They speed up reactions to reduce cost and they are not used up so can be used again.
• They lower energy demands, therefore less CO2 produced and less environmental impact.
• They also lower production costs.

• These are used inside petrol-engine cars and reduce the number of polluting gasses produced by the engines.
• They are made of ceramic material arranged in a honeycomb shape which is coated with platinum and rhodium.
• The shape of the converters give it a large surface area which means less of the reactants is used up – only small amounts of platinum and rhodium are needed.
• When the polluting gasses pass over the catalyst they trigger a series of chemical reactions that produce less harmful products:
  (i) Carbon Monoxide   +   Nitrogen Oxides   -->   Nitrogen   +   Carbon Dioxide
  (ii) Hydrocarbons   +   Nitrogen Oxides   -->   Nitrogen   +   Carbon Dioxide   +   Water

• The Maxwell-Boltzmann distribution is the shape formed on the graphs, which are used to show the distribution if energy amongst particles.

• The following things can be observed from the graphs:
  (1) No particles have zero energy.
  (2) Most particles have intermediate energy – the area around the peak of the curve.
  (3) A few particles have high energy – displayed in the right hand side of the curve.
  (4) The average energy is not the same as the most probable energy.

• There are several factors that will cause a change to occur in the shape of the Maxwell-Boltzmann distribution curve.

(1) Temperature – A higher temperature will lower the peak and move it to the right of the graph and the number of particles that reach the activation energy will increase

(2) Catalysts – With the use of a catalyst the activation energy needed is lowered meaning that the ‘minimum activation energy’ line is moved to the left

That's the end of the topic!

CLICK HERE TO LEARN MORE ABOUT OUR AS/A-LEVEL CHEMISTRY COURSES

Drafted by Bonnie (Chemistry)