Rate of reaction

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  • Created by: Sophie
  • Created on: 05-12-14 17:18
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  • Rates and Energy
    • Collision theory and surface area
      • Bigger surface area, more sides exposed to collide
        • Powder reacts more quickly than large lumps
      • Need enough activation energy to collide with
        • Minimum amount of energy they need to react
    • The effect of temperature
      • The particles have more energy
      • Move around more quickly
      • Also collide with more activation energy
        • Collisions more likely to result in a reaction
      • At normal temps. a rise of 10 degrees will double the rate of reactions
      • Increases the FREQUENCY of collisions
    • Effect of concentration/pressure
      • Same amount of particles in the same volume
        • More likely to collide
        • Dissolved particles are closer together
    • Effect of catalysts
      • Catalysts aren't used up
      • Can be used over and over again
      • Different reactions need different catalysts
      • Lower the activation energy
    • Exothermic / endothermic
      • Exothermic
        • Temperature of the surroundings increases
        • Combustion, neutralisation, oxidation
        • Transfers energy to the surroundings
      • Endothermic
        • Thermal decomposition
        • Take in energy from the surroundings
        • Some cause a decrease in temperature and others require a supply of energy
      • Energy can be transferred to or from the reacting substances in a reaction
    • Reversible reactions
      • If something is endothermic in one direction, it will be exothermic in the other
      • The amount of energy releases when the reaction goes in one direction is exactly equal to the energy absorbed in the opposite direction
    • Using energy transfers from reactions
      • Exothermic reactions can be used to heat things
        • Hand warmers and self heating cans
      • Endothermic changes can be used to cool things
        • Instant cold packs for sports injuries
    • How fast?
      • Can be found measuring how much of a reactant is used/product is formed against time taken
      • Can also be found by measuring the time taken for an amount of solid to appear
      • Steeper the gradient, faster the reaction

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