The stopwatch and prepare - Sample Essay

In this we were able to see how temperature effects the rate of reaction. A pale yellow precipitate of Sulphur was formed obscuring the cross and signifying that the experiment is over. As I increased the temperature of the solution of Sodium Thiosulphate the time taken for the cross to disappear decreased significantly. In Graph one, showing all the temps. used against time taken, the curve is negatively correlating. In Graph two, rate of reaction against temp. the graph shows that as you keep increasing temp the rate of reaction slows down as you can see that rate increases at a steeper rate at the beginning of the graph than at the end.

We can also see that there is a positive correlation curve, this is seen as temp is increased by ten degrees the rate doubles As I stated earlier this expt, produces a pale yellow sulphurous p. p. t which obscures the cross from view. The following equation explains why this is produced: Na S O +2HCl S + SO +2NaCl + H O Chemical reactions, like the one investigated here, take place as a result of collisions among reactant particles. By keeping all other factors affecting rate of reaction constant apart from temp. we can investigate how and why it affects the reaction rate.

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I conclude that the higher the temperature the faster the reaction takes place as temp is a factor that affects collision of particles. The higher the temp. the faster the particles move around resulting in more collisions between them. Also the higher the temp the more energetic and effective the collisions meaning that there are collisions where the particles contain enough energy to break existing covalent bonds. When these existing bonds within reactant particles break they form free atoms that can re-bond and form new products e. g. with H and Cl .

At a low temp only a few particles have sufficient energy to react on collision. As the temp increases, however the amount of particles with adequate energy to react increase, increasing the frequency of collision and the rate of reaction. Evaluation In my expt. the solution of Sodium Thiosulphate reacted with HCl to produce a pale yellow p. p. t of Sulphur which obscured the cross and made it possible for me to record when the they had stopped reacting and the expt was over. Sources of Error There were a number of different areas where errors occurred which can explain my anomalous results.

As the expt progressed I had to rely on the naked eye to determine whether the cross had disappeared or not, which is not an accurate method of collecting information.  When starting the stopwatch at the beginning and stopping it at the end, time is lost as it is impossible to both start the stopwatch and prepare the beginning of the expt at the same time single-handedly. This causes the recorded time measurements to be unreliable.  When recording the temp. of the Sodium Thiosulphate in preparation for the expt.



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