AS Chemistry OCR A - Rates of Reaction

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Collision Theory

  • Increase in concentration
    • Increase in amount of molecules per unit volume
    • Increases the frequency of collisions
  • Increase in pressure of a gas
    • Increase in amount of molecules per unit volume.
    • increases the frequency of collisions
  • Increase the temperature
    • Increases the energy of the molecules.
      • Increases the speed of the molecules
        • Increases the frequency of collisions
      • Increases the chance that colliding molecules have higher energy than the activation energy
        • Increases the rate of successful collisions 
  • Use of catalyst
    • Provides secondary route to the products with a lower activation energy.
    • Highten the chance that colliding molecules will have higher energy than the new activation energy.
    • Increases the rate of successful collisions.
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Collision Theory Cont.

  • Increase surface area of a solid.
    • Increase the amount of interfacing molecules.
      • Increase the frequency of collisions
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Boltzmann Distribution Graphs

(http://www.4college.co.uk/as/atm/rate.gif)

  • The area under the graph is the amount of molecules in the chemical system.
    • Stays the same
  • The shaded area shows the amount of molecules with activation energy.
  • The curve should start from the origin, as there are no molecules with no energy.
  • Catalysts provide a secondary route of reaction with lower activation energy.
    • Add a secondary marker to the left of activation energy labelled catalyst. 
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Boltzmann Distribution and Temperature

(http://puu.sh/nF9E5/a5bc1883b6.png)

  • Because the area under the graph remains constant:
    • As the temperature increases the height of the peak lowers and moves to the right.
    • As the temperature decreases the peak heightens and moves to the left.
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Concentration - Time graphs

  • There are two concentration time graphs.
    • Product (http://wpage.unina.it/petrilli/gifs/enzpt.gif)
    • Reactant    (http://puu.sh/nF9SL/0e38b0f4dc.jpg)
  • The gradient of the curve is the rate of reaction.
  • Concentration of product increases as the reaction happens.
  • Concentration of reactant decreases as the reaction happens.
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