Lesson: Rate Laws from Initial Rates

In this lesson, we will learn how to use measurements of initial rate to deduce the rate law of a reaction and the order of reaction for each reactant.

Worksheet: 5 Questions

Q1:

In a reaction between compounds A and B , quadrupling the concentration of A doubles the rate of reaction. However, doubling the concentration of reactant B increases the rate by a factor of 8.

What is the order of reaction with respect to A ?

What is the order of reaction with respect to B ?

Q2:

Hypochlorite ( C l O ) and iodide ions react to form hypoiodite ( I O ) and chloride ions: The initial rate of reaction was measured at three different reactant concentrations, as shown in the table.

[ C l O ] (M) [ I ] (M) Initial Rate (M/s)
4 . 0 0 × 1 0 3 2 . 0 0 × 1 0 3 1 . 8 4 × 1 0 3
2 . 0 0 × 1 0 3 4 . 0 0 × 1 0 3 9 . 2 0 × 1 0 4
2 . 0 0 × 1 0 3 2 . 0 0 × 1 0 3 4 . 6 0 × 1 0 4

Determine the rate law for this reaction.

Determine the appropriate units for the rate constant of this reaction, 𝑘 .

Expressing concentrations in molars and time in seconds, estimate, to 3 significant figures, the numerical value of the rate constant, 𝑘 .

Q3:

Nitric oxide reacts with chlorine to form nitrosyl chloride : The initial rate of reaction of nitric oxide was measured at three different reactant concentrations, as shown in the table.

(M) (M) Initial Rate (M/s)
0.100 0.100
0.100 0.150
0.150 0.100

Determine the rate law for this reaction.

Determine the appropriate unit for the rate constant of this reaction, .

Expressing concentrations in units of molars and times in units of seconds, estimate, to 3 significant figures, the numerical value of the rate constant, .

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