Experiment 19: Kinetics : the Rate of an Experiment

March 17, 2013 March 17, 2013 Name : Ryan annasdass arokiasamy ID : 1206875 Group Members : Chan Pei Qie,Chong Ven Yen Name : Ryan annasdass arokiasamy ID : 1206875 Group Members : Chan Pei Qie,Chong Ven Yen experiment 19 kinetics : the study of a chemical reaction experiment 19 kinetics : the study of a chemical reaction Results Part A [I-] / mol dm-3| [S2O82-] / mol dm-3| [S2O32-] / mol dm-3| Time /s| Rate of I2 formation / mol dm-3 s-1| 0. 2| 0. 2| 0. 01| 1. 25| 0. 1600| 0. 2| 0. 15| 0. 01| 13. 37| 0. 0150| 0. 2| 0. 10| 0. 01| 26. 00| 0. 0077| 0. 2| 0. 05| 0. 01| 66. 5| 0. 00075| Part B [I-] / mol dm-3| [S2O82-] / mol dm-3| [S2O32-] / mol dm-3| Time /s| Rate of I2 formation / mol dm-3| 0. 2| 0. 2| 0. 01| 3. 45| 0. 0580| 0. 15| 0. 2| 0. 01| 7. 56| 0. 0198| 0. 10| 0. 2| 0. 01| 9. 06| 0. 0110| 0. 05| 0. 2| 0. 01| 23. 91| 0. 0021| Part C Initial temperature/ OC| Final temperature/ OC| Time t /s| Rate of I2 formation / mol dm-3| 1/T (1/K)| Log t | 15| 21| 29| 0. 00690| 0. 003472| 1. 462| 24| 25| 20| 0. 01000| 0. 003367| 1. 301| 35| 42| 13| 0. 01538| 0. 003247| 1. 114| 45| 40| 8| 0. 02500| 0. 003145| 0. 903| Calculations & Questions

Associated essay: Measuring Reaction Rate Using Volume of Gas Produced

The effect of temperature is that it increases the rate of reaction, observed here by the higher temperatures giving a much faster reaction time a) Is reaction (2) fast or slow with respect to reaction (1)? Explain your reasoning or record any test you do to help reach your conclusion Reaction (2) is fast with respect to reaction (1). Reaction (2): I2+2 S2O32-> 2 I-+ S4O62- occurs extremely fast, I2 formed in the reaction is consumed immediately and when the limiting agent S2O32- is used up, I2 reacts with the starch indicator to form a blue color solution. ) Does reaction (1) or (2) control the time required for the blue colour to appear? Reaction (1): 2I-+ S2O82->I2+2SO42- controls the time required for the blue colour to appear as it is the I2 that will react with the starch indicator to produce the blue color solution to appear c) Calculate the rate of formation of I2 in mol dm-3 s-1 for each experiment at room temperature and plot this rate i) Against [S2O82-] at constant [I-] ii) Against [I-] at constant [S2O82-] The rate of formation of I2 can be calculated by calculating of the rate of change of the thiosulphate ion over the time taken Rate of formation of I2=? I2]t d) What are the shapes of these plots? They are straight line graphs ,with the y axis directly proportional to the x axis e) What is the significance of this? This shows that the rate is directly proportional to the concentration of [I-] and [S2O82-] and by calculating the gradient of the graph we will obtain the rate of reaction. f) Write the rate equation for reaction (1) d[I2]dt=k[S2O82-] And calculate the rate constant , k Rate = k[I-][S2O82-] k = Rate / [I-][S2O82-] k = slope / [S2O82-] k = [(0. 015-0. 0008)/(0. 15-0. 05)]

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Secondly, there were separate measuring cylinders prepared for each solution as to not mix 2 solutions in a measuring cylinder to avoid any reactions. The persulphate was poured in rapidly as this is an extremely fast step and has to be poured all at once. Finally,when diluting the persulphate solution, it was done as accurately as possible in order to avoid a wrong concentration instead of the one intended. Conclusion Based on the experiment done as well as the analysis of the results and after doing further results, we have learned that the activation energy of the reaction is 32. 73 kJ.

Furthermore, we have gained an insight into the kinetics of a reaction, its rate, the rate constants as well as the rate of reaction. References: Martin S. Silberberg, Chemistry the Molecular Nature of Matter and Change, Fifth Edition, McGraw Hill, 2005. F. Albert Cotton, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann, Advanced Inorganic Chemistry, Sixth edition, John Wiley& Son. 1999. F. Albert Cotton, Geoffrey Wilkinson, Paul L. Gaus, Basic Inorganic Chemistry, Third Edition, John Wiley& Son. 1995. John C. Kotz, Paul M. Treichel, and Gabriela C. Weaver, Chemistry and Chemical Reactivity, Sixth Edition, Thomson 2006.

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