Rates of Reaction

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Measuring the Rate

Rate of reaction = How far a reaction proceeds in a given time

You can measure the rate by:

  • Using a stopwatch to time  how long it takes to reach a certain point
  • Using a gas cylinder to measure how much gas is produced in a given amount of time
  • Counting bubbles given off in a given amount of time
  • Measuring the weight before and after
  • Measuring the precipate formed
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Collision Theory

  • Reactions take place when particles collide with a certain amount of energy
  • The minimum amount of energy needed for the particles to react is called the activation energy and is different for each reaction.
  • If particles dont have enough energy, they wont be able to react

The rate depends on:

  • Frequency of collisions between particles
  • Amount of energy with which the particles collide

You can increase the rate by:

  • Increasing temperature
  • Increasing the surface area
  • Concentration/ Pressure
  • Use of a catalyst

The rate of reaction is fastest at the beginning where there is 100% of reactant, so the frequency on collisions is very high. The rate stops when the line on a graph levels out as there are no reactants left so the frequency of collisions is 0%

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Factors affecting Rates of Reaction

Surface area:

  • Smaller objects mean a larger surface area
  • A larger surface area means that more of the reactant can react at the same time, so the frequency of collisions is higher.

Temperature:

  • The higher the temperature, the faster the rate as the particles have more kinetic energy so the frequency of collisions increases
  • Often a 10 degree temp increase means the rate doubles- linear relationship

Catalysts:

  • A substance that increases the rate of a reaction but isnt used up in the reaction
  • They lower the activation energy needed so the frequency of collisions increases

Catalysts can be used in: Biological washing powders, Medicine, Biodiesel, Cars, Slimming/ Baby food

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Factors affecting Rates of Reaction

Concentration:

  • Dilute solution: a small amount of solute in a given amount of solution
  • Concentrated solution: a large amount of solute in a given amount of solution
  • The units of concentration are mol/dm
  • When the concentration/ pressurre are higher, the rate is faster because the frequency of collisions is higher

To calculate the rate of reaction from a graph you divide the time by the amount of product made

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