The Effect of Concentration on the Rate of Reaction :: GCSE Chemistry Coursework Investigation

The effect of concentration on the rate of reaction between sodium thiosulphate and dilute hydrochloric acid This investigation is about rates of reaction and what affects them. In this case I am going to look at hydrochloric acid and sodium thiosulphate which is a precipitation reaction causing the solution to go 'cloudy'. They react as in the equations below: sodium thiosulphate + hydrochloric acid -> sodium chloride + sulphur + sulphur dioxide + water Na2S2O3(aq) + 2HCl(aq) -> 2NaCl(aq) + S(s) + SO2(g) + H2O(l) A reaction will only occur where the particles of the reactants meet and combine. This is called the collision theory. For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the rate of reaction can be achieved by increasing the frequency of collisions. Therefore to increase the rate of reaction it is necessary to cause more particles to collide harder and collide more often. There are several ways to do this and these make up the factors for this experiment. They are listed below along with predictions as to their affect on the reaction. Possible Factors To make sure I carry out a fair test I will only change the concentration of sodium thiosulphate. I will keep the following factors the same. Increasing the pressure. By reducing the volume in which the same amount of particles exist the pressure is increased. Once the same number of particles are in a smaller area there is less space in which to move and so the particles are more likely to hit each other. It is therefore possible to predict that increasing the pressure will result in an increase in the rate of reaction. I will not test this variable because we don't have the facilities to test it. However pressure is a continuous variable. Catalyst. A catalyst is a separate substance that speeds up a reaction. After the reaction has happened it gets left behind. This makes this variable unsuitable for the type of experiment I am going to do. Temperature. By giving the particles extra energy they will move faster. This means that they cover more ground and are therefore more