6.02 – Rate Laws

Understand how rates are determined is important, but we need to be able to describe how each reactant contributes to the overall rate of a reaction.  For this, we will determine rate equations, known as rate laws, and the order (exponent) for each reactant.

Lesson Objectives

  • Explain the form and meaning of a rate law, including the ideas of reaction order and rate constant. (14.3)
  • Determine the rate law and rate constant for a reaction from a series of experiments given the measured rates for various concentrations of reactants. (14.3)

To become familiar with the topics presented in this mission, view the slides below and take note of the key ideas.  These are from section 14.3 of your text.

Now work through the practice problems, and post your work to OneNote.

For additional examples, view the slides below, which include more practice problems.

Work out these mastery problems and check your answers in OneNote.  Post your work when finished, including any corrections.  These questions are from the text.

14.30  The reaction 2 ClO2(aq) + 2 OH(aq) → ClO3(aq) + ClO2(aq) + H2O(l) was studied with the following results:

Trial [ClO2] [OH] Rate (M/s)
1 0.060 0.030 0.0248
2 0.020 0.030 0.00276
3 0.020 0.090 0.00828

(a) Determine the rate law for the reaction.

(b) Calculate the rate constant with proper units.

(c) Calculate the rate when [ClO2] = 0.100 M and [OH] = 0.050 M.


14.34  Consider the reaction of peroxydisulfate ion (S2O82−) with iodide ion (I) in aqueous solution:

At a particular temperature the initial rate of disappearance of S2O82 varies with reactant concentrations in the following manner:

Trial [S2O82-] [I] Rate (M/s)
1 0.018 0.036 2.6 × 10–6
2 0.027 0.036 3.9 × 10–6
3 0.036 0.054 7.8 × 10–6
4 0.050 0.072 1.4 × 10–5

(a) Determine the rate law for the reaction and state the units of the rate constant.

(b) What is the average value of the rate constant for the disappearance of S2O82− based on the four sets of data?

(c) How is the rate of disappearance of S2O82− related to the rate of disappearance of I?

(d) What is the rate of disappearance of I when [S2O82− ]=0.025 M and [I] = 0.050 M?


2001 FRQ #6

Way to go Visitor!  Keep up the hard work :)