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Determining the Order of Reaction: With Respect to Potassium Iodide

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Introduction

Determining the Order of Reaction: With Respect to Potassium Iodide Now I have completed my experiments, I have all the data needed to calculate the order of reaction in relation to Potassium Iodide. As earlier highlighted in my research, the rate equation is: m = order of reaction with respect to reactant A n = order of reaction with respect to reactant B In order to follow my calculations below, you may need to refer back to the relevant graph in the section titled Results, alternatively I have created a computerised version of the same graph and results table overleaf. After I plotted the graph against concentration of Potassium Iodide, (overleaf), I analysed it against the order graphs to see which it matched most closely, I noticed the line of best fit was very similar to the graph of first order. I can also support this with points off the graph: Concentration of KI (mol dm-3) Rate (mol dm-3s-1) As seen above, when the concentration doubles so does the rate of reaction. Henceforth the rate of reaction is directly proportional to the concentration. Therefore: [I-]1 Determining the Order of Reaction: With Respect to Hydrogen Peroxide In order to follow my calculations below, you may need to refer back to the relevant graph in the section titled Results, alternatively I have created a computerised version of the same graph and results table overleaf. ...read more.

Middle

This is called the rate constant, its value changes with temperature. Using my results at a certain temperature I should be able to calculate a value for 'k'. In this experiment I varied the temperatures, while the concentration of all reactants was kept the same throughout. Hence the only variable was temperature. From the calculations made it is clear that the value of k does not change with a change in concentration, however with a change in temperature it does. This is positive as my research had told me that the value of k only changes with temperature and my results back this up. The Reaction Mechanism: Many reaction mechanisms involve numerous different steps. The rate equation I have just calculated gives me the information needed to determine the slowest step in the reaction mechanism, often referred to as the rate determining step. Below is the rate equation I calculated. Rate = k [I-]1 [H2O2]1 [H+]0 This states that the reaction is first order with respect to hydrogen peroxide, first order with respect with respect to iodide ions and zero order with respect to hydrogen ions. Therefore the rate equation can also be written as. ...read more.

Conclusion

Therefore I can analyse the number of particles with activation enthalpy at temperatures with a 10K difference. To do this I will use the following equation. At 20oC (293.15K) the number of particles with activation enthalpy is: At 30oC (303.15K) the number of particles with activation enthalpy is: As visible there is not a double in the number of particles with activation enthalpy, for a double there would be a 100% percentage increase. However these unpredicted results could be due to an error in equipment which I will later discuss. To test if this is due to an error I shall work out the number of particles with activation enthalpy at two different temperatures with a 10K difference. At 40oC (313.15K) the number of particles with activation enthalpy is: At 50oC (323.15K) the number of particles with activation enthalpy is: Once again the number of particles with activation enthalpy does not double with a 10K increase in temperature. My results seem to suggest a 70% increase rather than a 100%. These results can be explained due to percentage error of equipment I used and also human error. I shall examine this in my evaluation. If the results of my experiment had worked as the Maxwell-Boltzman Curves suggest then my results would have been as below: ...read more.

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