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To Investigate Rates of Reaction

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Chemistry Coursework- To Investigate Rates of Reaction Plan The rate of reaction is the speed at which a reaction takes place. For a reaction to occur, bonds must be broken. A certain amount of energy is needed to do this, known as the activation energy (Ea). The kinetic theory states that all matter is in a constant state of movement, and due to this, particles collide. These collisions produce energy, and when there is enough, the bonds of a molecule are broken. The rate of a reaction is effected by three main factors: 1. The concentration of the reactants- with a higher concentration of particles, there are more chances for collisions to occur. 2. The temperature at which the reaction takes place- at a higher temperature, particles have more kinetic energy, so there are more collisions, and they are more energetic. 3. If a catalyst is used, it provides a reaction path that requires a lower activation energy. However, I will just be looking at the first two, concentration and temperature. I have chosen to use the reaction between sodium thiosulphate and hydrochloric acid. Sodium Thiosulphate + Hydrochloric Acid ? Sodium Chloride + Sulphur Dioxide + Water + Sulphur Na2S2O3(aq) + 2HCl(aq) ? 2NaCl(aq) + SO2(g) + H2O(l) + S(s) This is because this reaction takes a suitable amount of time to occur, when the right concentrations are used. ...read more.


Results Below is a list of results for the concentration experiment: I kept the temperature at room temperature. Concentration (g/dm�) Result 1 (secs) Result 2 (secs) Result 3 (if necessary) Average (secs) Rate x 1000 (s-1) 10 194.81 203.45 - 199.13 5.02 15 96.91 99.99 - 98.45 10.16 20 87.91 96.33 - 92.12 10.86 25 77.88 81.65 - 79.77 12.53 30 64.56 63.59 - 64.08 15.61 40 47.22 48.00 - 47.61 21.00 50 37.83 39.73 - 38.78 25.79 Below is a list of results for the temperature experiment: I kept the concentration at 25g/dm�. Temperature 1 (oC) Result 1 (secs) Temperature 2 (oC) Result 2 (secs) Average Temperature (oC) Average Time (secs) Rate x 1000 (s-1) 16 (room) 77.88 16 81.65 16 79.77 12.54 25 33.84 23 39.78 24 36.81 27.17 35 21.70 34 27.39 34.5 24.55 40.73 45 12.76 44 16.32 44.5 14.54 68.78 56 11.51 56 10.50 56 11.01 90.83 64 7.88 66 7.91 65 7.90 126.58 86 4.86 83 6.23 84.5 5.55 180.18 For this experiment, I am measuring rates of reaction, the speed at which the reaction takes place. However it is not possible to measure the rate directly; I must measure the time, and then convert it into rate. To do this, I use the formula: Rate = 1 / Time However, this formula gives you a very small number, which is had to plot a graph of. ...read more.


I think the evidence for the concentration experiment was reliable enough to support the conclusion. I had a fairly wide range of results, which were in an obvious to spot pattern. When I repeated the readings, the difference was less than 20%, which was the amount of difference I said I would need to decide to repeat the reading a third time. I don't feel I would like to repeat any results again using the apparatus I had, because I feel I got almost the best results I could have in the circumstances. I don't think that the evidence I obtained for the temperature experiment was reliable enough to support the conclusion. I found that the results were lower than I expected. For example, when I was expecting a double in the rate, due to the temperature rising 10oC, I only got a rise in rate of below 50% (see example in analysis). The cause of this is as I explained above. If I were to do further work, I would study the effect of a catalyst on the rate of reaction, looking at how different amount of a catalyst present in the reaction changed the rate. I would keep the amounts of the other reactants (sodium thiosulphate and hydrochloric acid) the same. Another thing I could investigate would be rates of reaction a solid and a liquid, although I would need an accurate way to measure surface area. I could use one solid, and see how its surface area affected the rate of reaction. ...read more.

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