Worksheet: Rate Laws from Initial Rates

In this worksheet, we will practice using measurements of initial rate to deduce the rate law of a reaction and the order of reaction for each reactant.

Q1:

In a reaction between compounds A and B , doubling the concentration of A increases the rate of reaction by a factor of 4. However, tripling the concentration of reactant B increases the rate by a factor of 3.

What is the order of reaction with respect to A ?

What is the order of reaction with respect to B ?

Q2:

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 ?

  • A4
  • B2
  • C 1 4
  • D 1 2
  • E1

What is the order of reaction with respect to B ?

Q3:

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 2 . 0 0 × 1 0 1 . 8 4 × 1 0
2 . 0 0 × 1 0 4 . 0 0 × 1 0 9 . 2 0 × 1 0
2 . 0 0 × 1 0 2 . 0 0 × 1 0 4 . 6 0 × 1 0

Determine the rate law for this reaction.

  • ARate = 𝑘 [ I ] 2
  • BRate = 𝑘 [ C l O ] [ I ] 2
  • CRate = 𝑘 [ C l O ] [ I ] 2 2
  • D Rate = 𝑘 [ C l O ] [ I ] 2
  • ERate = 𝑘 [ C l O ] [ I ]

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

  • A s−1
  • B L3/mol3⋅s
  • C L/mol⋅s
  • D M/s
  • E L2/mol2⋅s

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

  • A 2 . 8 8 × 1 0
  • B 1 . 1 5 × 1 0
  • C 1 . 1 5 × 1 0
  • D 5 . 7 5 × 1 0
  • E 4 . 6 0 × 1 0

Q4:

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.

  • ARate =
  • BRate =
  • CRate =
  • D Rate =
  • ERate =

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

  • A L3/mol3⋅s
  • B s−1
  • C M/s
  • D L2/mol2⋅s
  • E L/mol⋅s

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

Q5:

Time (s) 4.00 8.00 12.0 16.0 20.0
[ A ] (M) 0.220 0.144 0.110 0.088 0.074

By plotting suitable functions of the tabulated data, determine the appropriate unit for the rate constant of this reaction.

  • A s−1
  • B L2/mol2⋅s
  • C L3/mol3⋅s
  • D M/s
  • E L/mol⋅s

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

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