CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

General Chemistry 101/102General Chemistry 101/102Laboratory ManualLaboratory Manual

University of North Carolina at WilmingtonUniversity of North Carolina at Wilmington

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• PurposePurpose To study the effect of temperature on the To study the effect of temperature on the reaction reaction

raterate and the and the reaction rate constant (k)reaction rate constant (k) of a chemical of a chemical reaction and to determine the value of the reaction and to determine the value of the activation activation energy (Eenergy (Eaa)) for the reaction. for the reaction.

• Safety ConsiderationsSafety Considerations Wash your hands thoroughly after handling Wash your hands thoroughly after handling

chemical reagents and before leaving the lab.chemical reagents and before leaving the lab. All chemical wastes should be placed in the All chemical wastes should be placed in the

labeled jar in the hood.labeled jar in the hood.

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• BackgroundBackground The chemical reaction being studied in this The chemical reaction being studied in this

experiment is:experiment is:

6 I6 I-- + BrO + BrO33-- + 6 H + 6 H++ 3 I 3 I22 + Br + Br -- + 3 H + 3 H22OO

In the previous experiment, you determined the In the previous experiment, you determined the rate law for this reaction to be:rate law for this reaction to be:

Rate = k [IRate = k [I--] [BrO] [BrO33--] [H] [H++]]22

The value of the rate constant (k) depends on the The value of the rate constant (k) depends on the temperature. The relationship between rate constant temperature. The relationship between rate constant and temperature is given by the and temperature is given by the Arrhenius EquationArrhenius Equation

k = Aek = Ae-Ea/RT-Ea/RT

bromate ion

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• BackgroundBackground

k = Aek = Ae-Ea/RT-Ea/RTrate constantrate constant

frequency frequency factorfactor

activation activation energyenergy

Idea Gas constant Idea Gas constant (8.31 J/K·mol)(8.31 J/K·mol)

temperature (K)temperature (K)

Taking the log of both sides of the Arrhenius Taking the log of both sides of the Arrhenius Equation transforms it into a linear equation:Equation transforms it into a linear equation:

ln k = + ln Aln k = + ln A- E- Eaa

RTRT

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• BackgroundBackground The activation energy for a reaction can be found The activation energy for a reaction can be found

by measuring the value of k at several different by measuring the value of k at several different temperatures and then plotting ln k vs. 1/Ttemperatures and then plotting ln k vs. 1/T

ln A

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• ProcedureProcedure Each trial is performed at a different temperature Each trial is performed at a different temperature

(approximately 0 ºC, 10 ºC, 25 ºC, and 40 ºC). (approximately 0 ºC, 10 ºC, 25 ºC, and 40 ºC).

Allow both flasks to reach the desired temperature Allow both flasks to reach the desired temperature before combining them into flask “A”. Keep flask “A” before combining them into flask “A”. Keep flask “A” at the desired temperature during the reaction. at the desired temperature during the reaction. Record the time it takes for the blue color to appearRecord the time it takes for the blue color to appear. .

B

Add 4 drops of Add 4 drops of starch to flask “B”starch to flask “B”

Measure the quantities shown in Table 1 into flasks Measure the quantities shown in Table 1 into flasks labeled “A” and “B”. labeled “A” and “B”.

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• CalculationsCalculations A sample calculation for k is shown below.A sample calculation for k is shown below.

Rate = = k [IRate = = k [I--] [BrO] [BrO33--] [H] [H++]]22

tt

3.3 x 103.3 x 10-5-5 M M

k =k =t [It [I--][BrO][BrO33

--][H][H++]]22

3.3 x 103.3 x 10-5-5 M M

k =k =(180 s)(0.0020 M)(0.0080 M)(.020 M)(180 s)(0.0020 M)(0.0080 M)(.020 M)22

3.3 x 103.3 x 10-5-5 M M

k = 29 Lk = 29 L33/mol/mol33·s·s

CHM 101/102CHM 101/102

Laboratory ManualLaboratory ManualLaboratory Manual

Temperature and Reaction RateTemperature and Reaction Rate

• CalculationsCalculations Enter your data into an Excel spreadsheet as Enter your data into an Excel spreadsheet as

shown below and use GraphData to determine the shown below and use GraphData to determine the slope of the line.slope of the line.