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Investigation to determine whether agitation has an effect on the activation energy of a reaction.

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Introduction

Investigation to determine whether agitation has an effect on the activation energy of a reaction Activation energy is the minimum energy that a molecular collision must possess if the molecules are to react. The activation energy for a certain reaction can be calculated using the arrhenius equation if the dependence of the reaction rate on temperature is known. How to work out the activation energy of a reaction from the arrhenius equation: The Arrhenius equation: ln k = constant - EA / R (1/T) Where k is the rate constant of the reaction, R is the gas constant, 8.31J K-1 mol-1 EA is called the activation energy of the reaction, in J mol-1 T is the temperature in kelvins To work out the activation energy a graph of ln (rate) against 1/T /K-1 must be plotted. The graph would look like this: 1 / T K-1 ln(rate) The gradient of the graph = -EA / R Therefore the activation energy = the gradient of the graph multiplied by the gas constant. Method: Ideally I would like to conduct experiments varying the amount of agitation in a reaction, unfortunately the magnetic stirrer has only one speed, and so I am going to conduct some experiments using a magnetic stirrer and some without. I hope to find out whether the stirring has an effect on the activation energy. ...read more.

Middle

when the temperature at the start was much above room temperature it decreased through the course of the reaction because energy was lost to the surroundings. I would not be able to draw any sufficient conclusions from these results as they are too varied. I will need to repeat the experiment again using a water trough filled with water around the conical flask. This trough will sit on top of the magnetic stirrer and the conical flask will be supported around the neck with a clamp stand. I will heat the acid in a water bath to the desired temperature and I will place the conical flask in the trough that will also contain water of the desired temperature so that it will become the same temperature as the surroundings. When the acid has reached the desired temperature I will pour it into the conical flask. I am going to try and keep the temperature stable throughout the reaction by adding ice/hot water to the trough. I will again time the experiment until the volume of hydrogen produced has reached 20cm3. Results: Stirring? Start temp. (�c) End temp. (�c) Average temp. (�c) Time (s-1) y 10 15 12.5 83 n 9 14 11.5 140 y 20 25 22.5 48 n 20 22 21 120 y 31 34 32.5 39 n 31 33 32 90 y 40 39 39.5 27 n 40 38 39 42 y 50 48 49 21 n 50 51 50.5 34 I will now produce another table that will help me to plot a graph of ln(rate) ...read more.

Conclusion

Evaluation: Once I regulated the temperature of the acid I could see that my results were becoming more consistent. However I would have liked to repeat the experiments a couple more times for each temperature in order to get more accurate results. This may have also made the points on my graph in a much straighter line therefore reducing the error involved in finding the line of best-fit. The computer graph has proved to be more accurate in determining the gradient. I believe that my investigation has shown a rough value for the activation energy for hydrochloric acid. It has also shown that the agitation does not alter the activation energy, but serves to keep the rate of the reaction steady by helping to release the hydrogen bubbles clung to the magnesium metal. Conclusion: Agitation of the experiment between metals and acids does affect the activation energy of the reaction, this has been proven by my results which find the activation energies to be 28.23kj with agitation and 30.19kj without (computer graphs). The agitated experiment may have a lower value because the hydrogen bubbles on the surface of the magnesium would have been released by the agitation. In the experiment without agitation the hydrogen bubbles would have clung to the magnesium and inhibited any reaction between the hydrogen ions and the magnesium atoms on the surface. ...read more.

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