Reaction Rates

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  • Reaction Rates
    • 'The rate of reaction is the rate of change of the concentration of a reactant or product with time'
    • The rate of reaction is given by the gradient at any time
    • Effect of Concentration of rate of reaction
      • The rate of reaction increases as the concentration increases
        • This is because for chemical reactions to occur, an effective collision has to take place between the particles of the reactants
          • If the concentration of one or more reactants increases, then the particles are closer together and so they collide more often
      • For gases, increasing the pressure increases the concentration and therefore increases the rate of reaction
    • Activation Energy
      • 'Activation energy is the minimum energy that particles must have in order to react'
      • For reactions to occur the reacting particles must have at least a certain, minimum amount of energy called the activation energy to react
        • The energy is needed to begin to break existing bonds in the reactants before new bonds in the product can be formed
        • If the particles have insufficient energy, they simply bounce off each other unchanged
    • Effect of temperature on rates of reaction
      • Raising the temperature increases the rate of reaction due to;
        • As the temperature increases, so does the proportion of molecules that have an energy greater than the activation energy. So when the molecules collide, it is more likely to lead to a sucessful reaction
          • This is the main reason for rate increasing with temperature
      • As the temperature increases, the molecules are on average moving faster and therefore collide more often
        • This is generally a much smaller effect
      • Summary: As the temperature increases, there is an increased frequency of sucessful collisions
    • Catalysts
      • 'A catalyst increases the rate of reaction, but is not used up in the process. It does this by providing an alternative pathway of lower activation energy'
      • A higher proportion of molecules have a greater energy than the activation energy and so sucessful collisions are more frequent


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