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# Aim: To calculate the activation energy (EA) for the reaction between Br- and BrO3- in acid solution

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Introduction

Title: Calculation of Activation Energy of a Reaction Aim: To calculate the activation energy (EA) for the reaction between Br- and BrO3- in acid solution Introduction: Using the kinetic theory and probability theory, Maxwell and Boltzmann showed that the fraction of molecules with energy greater than EA was given by: Where: R is the gas constant = 8.314472 J K-1 mol-1 (in this experiment 2 decimal places will be used) T is the absolute temperature e is the exponential function EA is the activation energy of a reaction This suggests that at a given temperature The rate of reaction But as k, the rate constant for a reaction, is measured of the rare of reaction, we can write: k Savante Arrhenius developed this equation as: K= , also known as the Arrhenius equation This equation allows us to determine the activation energy of a reaction from the temperature dependence of its rate constant. Usually this is based on the above equation, rearranged by taking natural logarithms: lnK= + lnA In this experiment the following reaction will take place: 5Br-(aq) + BrO3- (aq) + 6H+ --> 3Br2(aq) + 3H2O(l) The reaction will take place in the presence of a fixed number of phenol and a small amount of methyl red indictor. The bromine produced will react with the phenol, until all the phenol has been consumed. ...read more.

Middle

68.0�C 341.0 0.00293255 3 0.33333333 -1.09861229 Table 2: Data needed for calculation of activation energy With the data above, the following graph can be made to calculate the activation energy of the reaction. Graph 1: 1/Absolute temperature vs. Natural log of rate of reaction Data processing: In the above graph the experimental data is plotted as well as a best fit line. In order to calculate the reaction's activation energy, the gradient must be calculated, a gradient for the best fit line is already calculated, however I shall also calculate the gradient for the experimental data as well. Gradient = or Gradient = = -9585 or -8045 (best fit line) R = 8.31 J K-1 mol-1 - EA = gradient R = -9585 (or -8045) 8.31 = -79651.35 (or -66853.95) EA = 79651.35 (or 66853.95) J moles-1 EA = 79.65135 (or 66.85395) kJ moles-1-->79.65 (or 66.85) kJ moles-1 Analysis: The reaction that took place in this experiment was between bromate and bromide ions in the presence of an acid, this reaction is summarized by the following equation: KBrO3 + 5KBr + 3H2SO4 3K2SO4 + 3H2O + 3Br2 In this reaction, the potassium and sulphate ions are not affected and therefore are called "spectator" ions. The ionic reaction is summarized by the following ionic equation: 5Br- + BrO3- + 6H+ 3Br2 + 3H2O The rate of this reaction is measured by measuring the rate at which bromine is produced. ...read more.

Conclusion

A few of these errors are described below along with some possible solutions: Error Solution The time at which the time was started and stopped is inaccurate due to human reactions. A quite unlikely solution would be to place the sample in a spectrophotometer and record absorbance vs. time. However, the temperature of the mixture will change once it is placed in the spectrophotometer. Determining whether the reaction has reached end point or not. This too can be solved using a spectrophotometer. Or perhaps a low-tech solution would be to place the boiling tube in front of a white tile. Often, the temperatures of the solutions varied. If the boiling tubes were left at longer periods of time in their respective baths, perhaps the boiling tubes would have equilibrated. The boiling tube left at room temperature is also in accurate as the temperature of the room varied. If this tube were also kept in a water bath, more accurate results would have been obtained. Another problem occurred when the solutions were mixed, one boiling tube had been taken out of the bath and exposed to the room temperature causing a slight change in temperature This is almost impossible to prevent. If perhaps the boiling tube had a sort of separator that could be removed externally then when both solutions reached the temperature of the bath the separator could be pulled out to avoid this source of error. ?? ?? ?? ?? Page | 1 ...read more.

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