Determination Of A Rate Law

Abstract

The rate of a chemical reaction may depend upon reactant concentrations, temperature, and the presence of catalysts. The results from the experiment show the orders are k [I]0[H2O2] and overall order is 1 and the reaction rate is 0.0500/О"t. The rate constant is 1.04 x 10-2 s-1.

Introduction

The rate of a chemical reaction may depend upon reactant concentrations, temperature, and the presence of catalysts. At a fixed temperature, the rate of a reaction may be mathematically described by a rate law. In this experiment the rate law for the chemical reaction, 2I + H2O2 пÑ" I2 + 2H2O. The reaction rate must be measured and the values of the constant (k) and order (p and q) for the rate law k [I]p [H2O2] q can be calculated.

Experimental

Table 1: Composition of experiment 1 solutions

Trial # Solution A Solution B

Buffer 0.3 M KI Starch 0.02 M Na2S2O3 DI Water 0.1 M H2O2 Temp Time

1 5.00mL 2.00mL 0.40mL 5.00mL 21.6mL 6.00mL 22Ð'oC 320s

2 5.00mL 4.00mL 0.40mL 5.00mL 19.6mL 6.00mL 21Ð'oC 255s

3 5.00mL 6.00mL 0.40mL 5.00mL 17.6mL 6.00mL 20.5Ð'oC 199s

4 5.00mL 6.00mL 0.40mL 5.00mL 13.6mL 10.00mL 20.5Ð'oC 120s

5 5.00mL 6.00mL 0.40mL 5.00mL 9.6mL 14.00ml 21Ð'oC 92s

Prepare each solution as indicated in Table 1. For solution A prepare in a clean beaker and swirl to mix thoroughly. Then add Solution B and begin timing the reaction. At the first sign of the blue color stop the clock. Record the time elapsed in seconds and the temp as done in Table 1.

Table 2: Composition of experiment 2 solutions

Trial # Solution A Solution B

Buffer 0.3 M KI Starch 0.02 M Na2S2O3 DI Water 0.1 M H2O2 Temp Time

1 5.00mL 6.00mL 0.40mL 5.00mL 13.6mL 10.00mL 1.5Ð'oC 568s

2 5.00mL 6.00mL 0.40mL 5.00mL 9.6mL 14.00mL 1.5Ð'oC 455s

3 5.00mL 2.00mL 0.40mL 5.00mL 21.6mL 6.00mL 42.0Ð'oC 127s

4 5.00mL 4.00mL 0.40mL 5.00mL 19.6mL 6.00mL 40.0Ð'oC 70s

5 5.00mL 6.00mL 0.40mL 5.00mL 17.6mL 6.00mL 31.0Ð'oC 90s

6 5.00mL 4.00mL 0.40mL 5.00mL 19.6mL 6.00mL 31.0Ð'oC 148s

Prepare two water baths one with ice water and the other should be set at 40Ð'oC. Prepare solution A and B as noted in Table 2. Place both solutions in the same water bath and wait for the temperatures to be the same. For trail 1 and 2 place in the ice bath, place both 3 and 4 in the heat bath till at 40Ð'oC, and lower the heat bath to 30Ð'oC then place 5 and 6 in the heat bath till they are at least 30Ð'oC. Record the temperature as is in the temp section as done in Table 2. Once they are at the same temperature add the two solutions and start timing till the combined solutions turn a blue color.

Calculations

Table 3: Rate Data for the reaction of I and H2O2

Trial # [I] M [H2O2]M Initial Rate (M/s)

1 0.015 0.015 1.56