Ch.13 - Chemical KineticsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution: Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g)
The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms.
Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step
Proposed mechanism II:
I2(g) → 2 I(g)          Fast
H2(g) + 2 I(g) → 2 HI(g)          Slow
Is the second of the proposed mechanisms valid?

Solution: Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g)The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms.Proposed mechanism I:

Problem

Consider the gas-phase reaction: H2(g) + I2(g) → 2 HI(g)
The reaction was experimentally determined to be first order in H2 and first order in I2. Consider the proposed mechanisms.
Proposed mechanism I: H2(g) + I2(g) → 2 HI(g) Single step
Proposed mechanism II:
I2(g) → 2 I(g)          Fast
H2(g) + 2 I(g) → 2 HI(g)          Slow

Is the second of the proposed mechanisms valid?

Solution

A reaction mechanism is a step-by-step sequence of elementary reactions by which overall chemical change occurs. Information about a reaction mechanism is often obtained through the use of chemical kinetics.


To solve this problem, we will go through the following steps:

  • Write a rate law for the first step of the mechanism II.
  • Eliminate any intermediates from this rate law.
  • Inspect its order to determine if its correct.


First, let’s see if the two equations in mechanism II add up to a balanced chemical equation.


Solution BlurView Complete Written Solution