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Temperature and Reaction Rate

Temperature and Reaction Rate. General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington. Safety Considerations. Wash your hands thoroughly after handling chemical reagents and before leaving the lab.

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Temperature and Reaction Rate

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  1. Temperature and Reaction Rate General Chemistry 101/102Laboratory ManualUniversity of North Carolina at Wilmington

  2. 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. Temperature and Reaction Rate • 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 (Ea) for the reaction.

  3. In the previous experiment, you determined the rate law for this reaction to be: Rate = k [I-] [BrO3-] [H+]2 Temperature and Reaction Rate • Background • The chemical reaction being studied in this experiment is: 6 I- + BrO3- + 6 H+ 3 I2 + Br - + 3 H2O bromate ion • 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

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

  5. ln A Temperature and Reaction Rate • 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

  6. Measure the quantities shown in Table 1 into flasks labeled “A” and “B”. B Add 4 drops of starch to flask “B” Temperature and Reaction Rate • 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.

  7. k = Rate = = k [I-] [BrO3-] [H+]2 3.3 x 10-5 M Dt [I-][BrO3-][H+]2 3.3 x 10-5 M Dt Temperature and Reaction Rate • Calculations • A sample calculation for k is shown below. 3.3 x 10-5 M k = (180 s)(0.0020 M)(0.0080 M)(.020 M)2 k = 29 L3/mol3·s

  8. Temperature and Reaction Rate • Calculations • Enter your data into an Excel spreadsheet as shown below and use GraphData to determine the slope of the line.

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