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Rates of Reaction

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Rates of Reaction Aim For the cause of this venture I will be performing an experiment within which my aim will be to determine the effect, concentration has on the rate of reaction. I will be undertaking an intense study between hydrochloric acid and sodium thiosulphate. sodium + hydrochloric sodium + sulphur + sulphur + water thiosulphate acid chloride dioxide Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + S(s) + SO2(g) + H 2O(l) The rate of reaction is the speed at which a reaction takes place. It is the rate of loss or formation of a product during a chemical reaction. In this case the rate of reaction will be measured upon the speed at which the solid sulphur is formed and thus the colourless solution goes cloudy. Prediction For a given reaction to take place, particles must collide with each other hard enough for a reaction to take place. However not all collisions result in a reaction, this is due to the energy barrier they must overcome. Only particles with enough energy to overcome that barrier will result in a reaction having collided with neighbouring particles. The energy contained by the particles is known as the 'activation energy'. This activation energy differs for each reaction. Furthermore, there are four main factors which influence the rate of a reaction. These four factors are the following: * Catalyst * Concentration * Surface area * Temperature Catalyst A catalyst is something which reduces the activation energy, therefore the rate of reaction increases. Thus a catalyst can be defined as something which increases the rate of reaction. A catalyst is never used up; it just simply decreases the activation energy required for the reaction to take place. Hence the reaction occurs much quicker and the rate of reaction is increased. A lot of chemical reactions are very slow; they have a slow rate of reaction. In such cases or in any other cases catalysts can be used to speed up reactions. ...read more.


Occasionally we did see a very odd results that did not compare well with the other results, we discarded these and repeated the readings to make sure the results remained precise. The average is what we recorded on the graph. We repeated the above for all the different concentration levels of HCl, as listed in the table above. Below is a small diagram explaining how we measured the rate of reaction: Look at cross through solution Timing how long it takes for the cross to disappear can be used to measure the rate of reaction; the lengthier the time, the slower the rate of reaction. The shorter the time, the quicker the rate of reaction. We will know approximately when the reaction has taken place; when the solution has become cloudy and the cross can no longer be seen: Results Below is a table showing the results we obtained from the experiment: Concentration of HCl (M) Take 1 (seconds) Take 2 (seconds) Take 3 (seconds) Average time (seconds) 2.d.p 0.1 140 145 147 144.00 0.2 71 115 113 99.67 0.3 99 104 101 101.33 0.4 87 92 90 89.67 0.5 82 86 85 84.33 0.6 80 78 78 78.67 0.7 75 77 76 76.00 0.8 70 73 74 72.33 0.9 69 70 72 70.33 1 69 70 70 69.67 Below is a graph with the above results plotted upon. The x-axis represents the time taken for the reaction, and the y-axis represent the varying concentrations of HCl. I have also hand-drawn the above graph on graph paper; this allows me to draw a much smoother curve. As can be seen from the above graph we did obtain an anomaly that does not fit in with the line of best curve, which I have circled. The only reason I could possibly think of as to why I obtained this anomaly is because we made a mistake somewhere when diluting down the concentration of HCl to 0.2M. ...read more.


However, if the temperature is decreased, then the kinetic energy is also decreased, which alternatively results in a slower rate of reaction. Below is a diagram explaining how this method would take place: For this investigation I would insert both reactants into the sealed conical flask and observe the final reading on the syringe starting from 0. I would record the amount of gas given off are certain intervals and work out the initial rate of reaction by reading of the graph that I have inserted with the diagram setup. Another factor I could change if I was to repeat the experiment, could be the concentration of the sodium thiosulphate and also the start and end concentrations of the HCl. I would also definitely carry out the experiment to 2M HCl rather than ending it at 1.0M. By doing this the straight could clearly be visible on the graph and my prediction could be backed up a lot more. I could have also gone up in 0.05M HCl rather than 0.1M HCl. I could also use a burette or an accurate pipette to measure the solutions, if the experiment was to be repeated.. By doing this the accuracy of the experiment would have been improved by a great deal. I believe I did have some experimental errors. For example referring back to the table on page 6, picking an example; when the concentration of HCl is 0.1M, the range between 'Take 1' and 'Take 3' is 7 (147 - 140). The highest fluctuation value is 140 from the average 144; 4/144 = 2.78%. So an idea of the experimental error as a percentage is 2.78%. Concentration of HCl (M) Take 1 (seconds) Take 2 (seconds) Take 3 (seconds) Average time (seconds) 0.1 140 145 147 144 This is not too bad, considering that the experiment was done in a very basic laboratory. Conclusively, I have managed to produce a curve on the graph and the points did fall on the curve. This shows that my results were fairly precise. ?? ?? ?? ?? ...read more.

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