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IB Chemistry HL 2.2.6 Hl Reaction Mechanisms Questions

Use real HL exam questions to evaluate proposed mechanisms against rate laws, stoichiometric data and the roles of intermediates and rate-determining steps.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Describe a reaction as a series of elementary steps and distinguish reactants, products, intermediates and catalysts from the proposed mechanism.
  • Identify the rate-determining step and derive the rate expression or stoichiometric consequence implied by the slow elementary step.
  • Evaluate a proposed mechanism by comparing its predicted rate law and overall equation with experimental kinetic and stoichiometric data, then support or reject it with a stated mismatch or match.

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Study 2.2.6 (HL)—Reaction mechanisms conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Chemistry HL 2.2.6 Hl Reaction Mechanisms Questions question 1

[Maximum number: 1]

The reaction between hydrogen and nitrogen monoxide is thought to proceed by the mechanism shown below.

2NO( g)⇌N2O2( g) fast equilibrium N2O2( g)+H2( g)→N2O( g)+H2O( g) slow reaction N2O( g)+H2( g)→N2( g)+H2O( g) fast reaction \begin{array}{ll} 2 \mathrm{NO}(\mathrm{~g}) \rightleftharpoons \mathrm{N}_{2} \mathrm{O}_{2}(\mathrm{~g}) & \text { fast equilibrium } \\ \mathrm{N}_{2} \mathrm{O}_{2}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) & \text { slow reaction } \\ \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) & \text { fast reaction } \end{array}

State, giving your reason, whether confirmation of the rate expression would prove that the mechanism given is correct.

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