CHM 101/102 Laboratory Manual Temperature and Reaction Rate General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Purpose Purpose  To study the effect of temperature on the reaction rate and the reaction rate constant (k) of a chemical reaction and to determine the value of the activation energy (E a ) for the reaction. Safety Considerations Safety Considerations  Wash your hands thoroughly after handling chemical reagents and before leaving the lab.  All chemical wastes should be placed in the labeled jar in the hood.

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Background Background  The chemical reaction being studied in this experiment is: 6 I - + BrO H + 3 I 2 + Br H 2 O  In the previous experiment, you determined the rate law for this reaction to be: Rate = k [I - ] [BrO 3 - ] [H + ] 2  The value of the rate constant (k) depends on the temperature. The relationship between rate constant and temperature is given by the Arrhenius Equation k = Ae -Ea/RT bromate ion

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Background Background k = Ae -Ea/RT rate constant frequency factor activation energy Idea Gas constant (8.31 J/K·mol) temperature (K)  Taking the log of both sides of the Arrhenius Equation transforms it into a linear equation: ln k = + ln A - E a RT

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Background Background  The activation energy for a reaction can be found by measuring the value of k at several different temperatures and then plotting ln k vs. 1/T ln A

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Procedure Procedure  Each trial is performed at a different temperature (approximately 0 ºC, 10 ºC, 25 ºC, and 40 ºC).  Allow both flasks to reach the desired temperature before combining them into flask “A”. Keep flask “A” at the desired temperature during the reaction. Record the time it takes for the blue color to appear. B Add 4 drops of starch to flask “B”  Measure the quantities shown in Table 1 into flasks labeled “A” and “B”.

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Calculations Calculations  A sample calculation for k is shown below. Rate = = k [I - ] [BrO 3 - ] [H + ] 2 tttt 3.3 x M k =  t [I - ][BrO 3 - ][H + ] x M k = (180 s)( M)( M)(.020 M) x M k = 29 L 3 /mol 3 ·s

CHM 101/102 Laboratory Manual Temperature and Reaction Rate Calculations Calculations  Enter your data into an Excel spreadsheet as shown below and use GraphData to determine the slope of the line.