To investigate one factor that will affect the rate of decomposition of hydrogen peroxide.

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Aim: To investigate one factor that will affect the rate of decomposition of hydrogen peroxide

  • The word equation for the decomposition of hydrogen peroxide is:

       Hydrogen peroxide      →      oxygen      +       water

              The chemical equation is:

                               2H  O   →    O   +  2 H O

  • The rate of reaction is the rate at which the reactants react or products are being formed in relation to the time factor.  The factors affecting the rate of reaction are as follows:
  1. Temperature
  2. Surface area
  3. Concentration if the reactants are liquid or pressure if the reactants are gases.
  4. Amount of catalyst
  5. Type of catalyst

  • The chosen factor: Concentration
  • When I increase the concentration of the reactant ( in this case hydrogen

      Peroxide) the rate of reaction will increase (in this case the rate of production

      oxygen).  The rate of reaction is directly proportional to the concentration.

      If I double the concentration, I expect that the rate of reaction will double as

      a result.

Prediction

The rate of reaction means the rate at which H  O (l) and O (g) are formed, which is the same as the rate at which H  O  (aq) is used up. We would measure the rate of this reaction as moles of hydrogen peroxide used up per second.

The rate of reaction for the decomposition of hydrogen peroxide

I look more closely at the decomposition of hydrogen peroxide in solution.  a particularly effective catalyst is the magnesium  oxide.

I intend to do an experiment to investigate the decomposition of hydrogen peroxide of different concentrations in the presence of catalyst magnesium oxide.  I will measure the total volume of oxygen given off at different times from the start of the experiment and plot a graph of this against time .This allows me to work out the rate of the reaction in cm³of oxygen.

The gradient of the graph gives me the rate of the reaction – the steeper the gradient the fester the reaction.  The reaction is at its fastest at the start, when the concentration of hydrogen peroxide in solution is high before any has been used up.  The graph gradually flattens out.  This is because, as the hydrogen peroxide is used up, its concentration falls. The lower the concentration, the slower the reaction.  Eventually, the graph is horizontal.  The gradient is zero,  and the reaction will come to a stop.  The rate of reaction at the start is called the initial rate.  I can find the initial rate by drawing a tangent to the curve at the point t=0, and measuring the gradient of this tangent.

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In each case, the concentration of the catalyst will be kept constant and all other conditions such as temperature.  The graph start off with differing gradients depends on the concentration of hydrogen peroxide I start with.  Now I am in a position to answer the question “How does the rate of reaction depends on the concentrations of hydrogen peroxide ?”.  I will plot the initial rate of reaction against concentration of hydrogen peroxide and I can arrive at the effect that it is a straight line graph.

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