Reaction Kinetics

Reaction Kinetics: Rate of Reaction

Of Tertiary-Butyl Bromide

Purpose: The purpose of this experiment is to find the order of t-BB graphically, to find the k (rate constant) at 0˚ C and at room temperature, also to find the Ea (activation energy).

Principles: Several different chemical kinetic principles were used in this experiment. The reaction rates of this chemical equation were determined experimentally. This then allowed the reaction mechanisms (i.e. orders of each component, rate constant, etc.). These mechanisms were ultimately determined to be compiled to form a rate law.

Rate = k[A]m[B]n

Integrated rate laws are used to determine concentrations of reactants at certain times. However, these integrated equations can only be used after the experimental data is collected. Temperature has an effect on the rates of reactions. Swedish chemist, Svante Arrhenius, discovered that the rate constant of a reaction increased logarithmically in proportion to the reciprocal of the absolute temperature. This is expressed mathematically as:

k = Ae-ΔE/RT

Method: 100 mL of water/ Isopropyl Alcohol were added to a 250 mL Earlenmeyer flask along with 15 drops of phenolphthalein. A buret was washed with soapy water and rinsed with 0.2 M NaOH. The buret was then filled to 0.00 mL. 2.00 mL of NaOH were added to the flask and it was placed into an ice-water bath.

t-BB was injected into the flask by the lab assistant with this exact time being noted. The exact time was recorded once again when the solution became colorless.

About two mL of NaOH were added to the solution and the time recorded when this became colorless. This was done until seven time readings were recorded. After the 7th addition of NaOH, the flask was removed from the ice bath and placed in a hot water bath for approximately ten minutes. The flask was then removed from the bath and cooled to room temperature. The solution was then titrated to a slight pink color. The volume reading of the burette was equal to the total base added during the experiment.

This experiment was repeated in duplicate at room temperature.

CH3 CH3

CH3 - C - Br + H2O  CH3 - C - OH

CH3 CH3

The complete procedure can be found at Blackboard.com under the Course Documents file labeled Reaction Kinetics.

Data: Vo : 102mL Start time: 9:22:25 binf : 21.61mL

A Number Time to Colorless Total Sec bt (mL) (binf -bt) 1 9:25:05 160 2.00mL 19.61

2 9:28:04 339 4.00mL 17.61

3 9:35:34 789 6.00mL 15.61

4 9:43:57 1292 7.50mL 14.11

5 9:49:11 1606 9.00mL 12.61

6 9:57:36 2111 10.5mL 11.11

7 10:07:12 2687 12.0mL 9.61

(Vo-bt) H lnH 1/H

104.0 .189 -1.67 5.29

106.0 .166 -1.80 6.02

108.0 .145 -1.93 6.90

109.5 .129 -2.05 7.75