Worksheet: Elementary and Rate-Determining Steps

In this worksheet, we will practice using the orders of reaction in a rate law to identify the rate-determining step in a multi-step reaction.

Q1:

Chlorine radicals from the decomposition of chlorofluoromethanes, such as CClF22, catalyze the decomposition of ozone (O3) in the atmosphere. One decomposition pathway involves three elementary reactions:

Reaction 1: OO+O32, rate constant =𝑘.

Reaction 2: O+ClO+ClO32, rate constant =𝑘.

Reaction 3: O+ClOO+Cl2, rate constant =𝑘.

Write a balanced chemical equation for the overall reaction.

  • A O + C l O + C l O 3 2
  • B 2 O + 2 C l 3 O + 2 C l O 3 2
  • C O 2 O 3 2
  • D O + 2 C l O + 2 C l O 3 2
  • E 2 O 3 O 3 2

Explain why chlorine radicals are catalysts in this reaction.

  • AReaction 2 converts chlorine radicals to ClO radicals, which are necessary to consume the O radicals produced in Reaction 1.
  • BChlorine radicals are consumed in Reaction 2 but regenerated in Reaction 3, so there is no net change in [Cl].
  • CReaction 2 converts chlorine radicals to ClO radicals, which are less stable than the O radicals produced in Reaction 1.
  • DChlorine radicals react in the rate-determining step, Reaction 2.
  • EThe reaction of O3 with chlorine radicals is faster than the decomposition Reaction 1.

Q2:

A reaction proceeds by the following two-step mechanism: The first elementary reaction is much slower than the second. What is the rate equation for the overall reaction?

  • ARate = 𝑘[A]2
  • BRate = 𝑘[A][B]2
  • CRate = 𝑘[B]2
  • DRate = 𝑘[A][B]2
  • ERate = 𝑘[A][B]22

Q3:

A reaction proceeds by the following three-step mechanism: The first elementary reaction is much slower than the second and the third. What is the rate equation for the overall reaction?

  • ARate = 𝑘[A][B]
  • BRate = 𝑘[A]
  • CRate = 𝑘[A][B]2
  • DRate = 𝑘[A][B]2
  • ERate = 𝑘[A][B]22

Q4:

An elementary reaction has the shown equation. A+2BC What is the rate equation for this reaction?

  • ARate = 𝑘[C][A][B]2
  • BRate = 𝑘[A][B]2
  • CRate = 𝑘([A]+2[B])
  • DRate = 𝑘[A][B]
  • ERate = 𝑘[C]([A]+2[B])

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.