This reaction can be used to analyze for iodide ion. IO3 –(aq) + 5I–(aq) + 6H+(aq) → 3I2(aq) + 3H2O( — Kinetics Chemistry Question
Problem Context
This reaction can be used to analyze for iodide ion.
IO3 –(aq) + 5I–(aq) + 6H+(aq) → 3I2(aq) + 3H2O(l)
When the rate of this reaction was studied at 25 °C, the results in the table were obtained.
Use these data to determine the order of the reaction with respect to each of these species. Outline your reasoning in each case.
i. I–
Model Answer
First order in I–. Compare the results of experiments 1 and 2 to see that the rate went up by a factor of 4 when the concentration of I– went up by 4.
ii. IO3 –
Model Answer
Second order in IO3 –. Compare the results of experiments 1 and 3 to see that the rate went up by 9 when the concentration of IO3 – went up by 3.
iii. H+
Model Answer
Second order in H+. Compare the results of experiments 1 and 4 to see that the rate went up by 4 when the concentration of H+ went up by 2.
Calculate the specific rate constant for this reaction and give its units.
Model Answer
rate = k[I–]1[IO3 –]2[H+]2
rate = k(0.01)1(0.10)2(0.01)2
Based on the kinetics, discuss the probability of this reaction occurring in a single step.
Model Answer
Reaction is very unlikely to occur in one step. That would require the simultaneous collision of five particles.
The kinetics of reactions are often studied under pseudo first-order conditions. Describe what is meant by the term pseudo first order and illustrate how the reaction conditions above would be changed so that the [I–] would be pseudo first order.
Model Answer
Pseudo-first order refers to carrying out a reaction under conditions such that only one reactant changes concentration. For this reaction, pseudo-first order kinetics can be established by having a large excess of [IO3 –] and [H+].
The activation energy for this reaction was found to be 84 kJ·mol–1 at 25 °C. How much faster would this reaction proceed if the activation energy were lowered by 10 kJ·mol–1 (for example, by using a suitable catalyst)?