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Experiment 18 Variation of Reaction Rate with Temperature Chemistry 1220 136 September 30th 2013 Raffeal Bennett Purpose The purpose of this experiment was to recognize the relationship between k reaction rate and Ea activation energy at the temperature at which the reaction occurs Procedure Refer to pages 53 54 of General Chemistry 1220 Laboratory Manual by The Ohio State University Department of Chemistry Hayden McNeil Publishing 2013 2014 Sample Calculations Graphs Please see attached graph Report Sheet Trial Temperature of Water Bath degrees Celsius 75 65 55 45 35 25 15 Time Elapsed when Methyl Red Faded seconds 23 8 41 0 63 1 147 0 242 0 430 0 880 0 1 2 3 4 5 6 7 Ln t 1 T 1 K 3 17 3 71 4 14 4 99 5 49 6 06 6 78 0 00289 0 00296 0 00305 0 00314 0 00325 0 00336 0 00347 Slope of best fit line 6138 Activation energy kJ mol 51 04 Discussion As the temperature of the solution decreased the reaction rate also decreased and the time it took for the reaction to be complete increased At 75 degC the reaction took about 23 8 seconds at 65 degC it took about 41 seconds at 55 degC it took about 63 1 seconds at 45 degC it took about 147 seconds at 35 degC it took about 242 seconds and 25 degC it took about 430 seconds and at 15 degC it took about 880 seconds Using the Arhenius equation it is clear that the value of k increases as T increases This is because increased temperature cause the e EaRT value to decrease therefore making the k value increase This means that at a higher temperature more molecules have the energy require to react Because the rate constant k is directly proportional to the reate of reaction increasing the value of k increases the rate of the overall reaction This is shown in the experiment because colder solutions took much longer to react that the warmer solutions As the temperature decreased by about 10 degC the time it took the solution to turn clear increased decreasing the rate of the reaction The fastest reactions lasted about 23 8 seconds and occurred in the 75 degC bath while the slowest reactions happened at 880 seconds in the 15 degC bath As the temperature decreased the time it took for the red color to face increased by more and more each time Based on the graph of lnt vs 1 T the Ea can be recorded from the slope of the graph multiplied by the constant of heat The slope of the graph was 6138 while the activation energy was 51 04 kJ mol An expected value for the activation energy is 45kJ to 60 kJ The value is expected to be within this range because the reaction was slow enough to time but fast enough to complete in a reasonable amount of time One source of error in this lab was the error of measurement Because the last digit in every measurement is an estimate no instrument is 100 accurate For example all buret readings could be off by 01 mL Another source of error was due to the inconsistency of temperature For example as the reaction was taking place in the water bath the temperature of the water was changing slightly This is especially true for the lower temperatures of water and the longer reaction rates It was very important to be consistent in this lab Such as letting the solution turn clear to the same extent in every trial with each different temperature Because each error only creates a small change in date these errors did not greatly affect the results of this lab These errors however can be noticed on the graph by points a little above or below the trendline The R 2 value was 9936 which shows very good correlation Conclusion In this lab the rate of reacton was recorded based on the time it took for the reaction to be complete at 7 different temperatures Solutions were placed in a water bath of a specific temeprature and the time it took for the red indicatior color to fade was recorded As the temperature of the water bath decreased the time required to complete the reaciton increased The reaction rate decreased because decreasing the temperature causes the rate constant k to decreased The temperature of a solution and the reaction rate are directly proportional Based on the Arhenius equation increaseing tmeperature causes k to increase therefore increasing the rate of reaction However incresing Ea causes k to decrease therefore decreasing the reaction rate The activation energy of this reaction was calculated to be 51 04 KJ mole

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