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Chemistry LibreTexts

Homework 5 (Due 4/15/16)

  • Page ID
    47375
  • Name: ______________________________

    Section: _____________________________

    Student ID#:__________________________

    Q5.1

    Write the differential rate laws describing the kinetics for the following mechanisms (make sure to denote the different rate constants):

    1. \( A \rightarrow B \rightarrow C\)
    2. \( A \rightleftharpoons B \rightarrow C\)
    3. \( A \rightarrow B \rightleftharpoons C\)
    4. \( A + B \rightarrow C \rightarrow D\) and \( A + D \rightarrow C\) and \( C \rightarrow A\)

    Q5.2

    For each example in Q5.1, how would you solve for the integrated rate laws. Make clear any approximations you may use and their applicability.

    Q5.3

    Although an increase in temperature results in an increase in kinetic energy, this increase in kinetic energy is not sufficient to explain the relationship between temperature and reaction rates. How does the activation energy relate to the chemical kinetics of a reaction? Why does an increase in temperature increase the reaction rate despite the fact that the average kinetic energy is still less than the activation energy?

    Q5.4

    For any given reaction, what is the relationship between the activation energy and each of the following?

    1. electrostatic repulsions
    2. bond formation in the activated complex
    3. the nature of the activated complex

    Q5.5

    What happens to the approximate rate of a reaction when the temperature of the reaction is increased from 20°C to 30°C? What happens to the reaction rate when the temperature is raised to 70°C? For a given reaction at room temperature (20°C), what is the shape of a plot of reaction rate versus temperature as the temperature is increased to 70°C?

    Q5.6

    Acetaldehyde, used in silvering mirrors and some perfumes, undergoes a second-order decomposition between 700 and 840 K. From the data in the following table, would you say that acetaldehyde follows the general rule that each 10 K increase in temperature doubles the reaction rate?

    T (K) k (M−1·s−1)
    720 0.024
    740 0.051
    760 0.105
    800 0.519

    Q5.7

    The data in the following table are the rate constants as a function of temperature for the dimerization of 1,3-butadiene. What is the activation energy for this reaction?

    T (K) k (M−1·min−1)
    529 1.4
    560 3.7
    600 25
    645 82