CHM 101/102
Temperature and Reaction Rate
General Chemistry 101/102
Laboratory Manual
University of North Carolina at Wilmington
Laboratory Manual
CHM 101/102
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.
•
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.
Laboratory Manual
CHM 101/102
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
 In the previous experiment, you determined the
rate law for this reaction to be:
Rate = k [I-] [BrO3-] [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
Laboratory Manual
CHM 101/102
Temperature and Reaction Rate
•
Background
rate constant
activation
energy
k = Ae-Ea/RT
frequency
factor
temperature (K)
Idea Gas constant
(8.31 J/K·mol)
 Taking the log of both sides of the Arrhenius
Equation transforms it into a linear equation:
ln k = - Ea + ln A
RT
Laboratory Manual
CHM 101/102
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
ln A
Laboratory Manual
CHM 101/102
Temperature and Reaction Rate
•
Procedure
 Each trial is performed at a different temperature
(approximately 0 ºC, 10 ºC, 25 ºC, and 40 ºC).
 Measure the quantities shown in Table 1 into flasks
labeled “A” and “B”.
B
Add 4 drops of
starch to flask “B”
 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.
Laboratory Manual
CHM 101/102
Temperature and Reaction Rate
•
Calculations
 A sample calculation for k is shown below.
-5 M
3.3
x
10
Rate =
= k [I-] [BrO3-] [H+]2
Dt
3.3 x 10-5 M
k=
Dt [I-][BrO3-][H+]2
3.3 x 10-5 M
k=
(180 s)(0.0020 M)(0.0080 M)(.020 M)2
k = 29 L3/mol3·s
Laboratory Manual
CHM 101/102
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.
Laboratory Manual