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Chemistry 14: 5-6

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Physical Reaction Mechanisms

Chapter 14: 5-6 Homework

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 14: Sections 5 and 6.

Study Notes
  1. 14.5 For a reaction to occur, the reacting molecules molecules must not only have sufficient kinetic energy of motion (activation energy Ea), they must also collide effectively. The rate of a reaction depends not only on temperature, where heat energy supplies the kinetic energy for the collision, but on the shape of the molecules, and the frequency of effective collisions.
  2. 14.6 A reaction mechanism may involve multiple reactions between initial reactants and their intermediate products to produce the final products of the overall reaction. The rate of a multiple-step reaction will be constrained to the rate of the slowest reaction step.

Key Formula

Concept Equation Notes
Arrhenius equation k   =   A e E a RT k: reaction rate
Ea: activation energy
R: gas constant
A: frequency factor (collision rate)
Arrhenius equation
Linear form
ln   k   =   E a R   1 T   +   ln   A  
Rate Mechanisms
Elementary StepRate equationMolecularity
A → productRate = k[A]unimolecullar
A + B → productRate = k[A][B]bimolecular
A + A → productRate = [A]2bimolecular
2A + b → productRate = k[A]2[B]trimolecular

Web Lecture

Read the following weblecture before chat: Reaction Mechanisms

Study Activity

Videos for Chapter 14: The Rates of Chemical Reactions

Review the Videos at Thinkwell Video Lessons.

  • Under "Chemical Kinetics"
    • Temperature and Rates
      • The Collision Model
      • The Arhennius Equation
    • Reaction Mechanisms
      • Determining the Rate Laws of Elementary Reactions
      • Calculating the Rate Laws of Multiple Step Reactions

Use the Rates of Reactions Simulation Rates of Reactions Simulation to perform Rate Experiments.

  • Accept the default initial scenario.
    • Set up the contain with 10 A and 10 BC molecules, and set the bonds and stopwatch to show.
    • Begin the experiment and start the stopwatch; let it run for 100 time units (or so). Do any reactions occur?
    • Increase the heat until the total average energy is just above the final potential energy. How long does it take for the reaction to reach midpoinmt (5 of each molecule)?
  • Reset the initial conditions, vary the experiment, and vary the concentrations.
    • What happens when the total average energy is above the peak potential energy from the start of the reaction?
    • What happens if you double the concentration and start with 20 of each reactant molecule?
    • What happens if you start with 10 of each reactant and each product molecule?
  • Draw some conclusions: how does temperature affect the reaction rate? How does concentration affect the reaction rate? Is the rate constant as long as there are reactants available?

Chat Preparation Activities

Chapter Quiz

(Aligns to) AP #11 GUIDED INQUIRY — Titration Methods — Phase II

Carry out the steps you outlined for one of your identified solutions. Based on your experience, adjust any procedures or data collection methods to increase your accuracy with your second solution, then analyze the second solution.