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5 Written Questions

5 Matching Questions

  1. The decomposition of dimethylether at 504°C is first order with a half-life of 1570. seconds. What fraction of an initial amount of dimethylether remains after 4710. seconds?
    a. 1/3
    b. 1/6
    c. 1/8
    d. 1/16
    e. 1/32
  2. The rate constant for a first-order reaction is 0.58 s−1 at 25°C. At what temperature would the rate constant have a value of 0.75 s−1? The activation energy is 84 kJ/mol and the universal gas constant = 8.314 J/mol•K.


    a. 30°C
    b. 300°K
    c. 298 K
    d. 301 K
    e. 310 K
  3. Which statement is false?
    a. If a reaction is thermodynamically spontaneous, it may occur rapidly.
    b. A fast reaction may be thermodynamically spontaneous.
    c. If a reaction is thermodynamically spontaneous, it may occur slowly.
    d. If a reaction is thermodynamically spontaneous, it must have a low activation energy.
    e. Rate of reaction is a kinetic quantity rather than a thermodynamic quantity.
  4. Consider the hypothetical reaction and rate data below. Determine the form of the rate-law expression (i.e., determine the values of a and b in rate = k[A]a[B]b) and also the value of the specific rate constant, k. Which of the answers below would be the initial rate of reaction for [A]initial = 0.40 M and [B]initial = 0.10 M?
    3A + 2B → Products

    Initial Rate of Reaction
    Run [A]initial [B]initial (moles per liter per second)
    1 0.10 M 0.10 M 4.0 × 10−4
    2 0.20 M 0.30 M 4.8 × 10−3
    3 0.30 M 0.10 M 3.6 × 10−3

    a. 1.6 × 10−4 M•s−1
    b. 3.4 × 10−3 M•s−1
    c. 1.2 × 10−3 M•s−1
    d. 4.8 × 10−4 M•s−1
    e. 6.4 × 10−3 M•s−1
  5. Suppose the reaction
    2AB + C2 → A2C + B2C
    occurs by the following mechanism.

    Step 1 AB + C2 → AC2 + B slow
    Step 2 B + AB → AB2 fast
    Step 3 AC2 + AB2 → A2C2 + B2 fast
    Step 4 A2C2 + B2 → A2C + B2C fast
    Overall 2 AB + C2 → A2C + B2C

    The rate law expression must be rate = ____.
    a. k[AB][C2]
    b. k[AB]2[C2]
    c. k[AB]2
    d. k[AB]
    e. k[C2]
  1. a c. 1/8
  2. b e. 6.4 × 10−3 M•s−1
  3. c b. 300°K
  4. d a. k[AB][C2]
  5. e d. If a reaction is thermodynamically spontaneous, it must have a low activation energy.

5 Multiple Choice Questions

  1. c. 0.0191 s−
  2. e. All molecular collisions result in a reaction.
  3. b. difficult to verify experimentally.
  4. e. a greater fraction of molecules possess the activation energy when they collide
  5. c. increases the rate at which equilibrium is reached without changing the equilibrium constant.

5 True/False Questions

  1. For the hypothetical reaction aA → products, the experimental data showed the following behavior (below). What is the reaction order with respect to reactant A?

    a. zero order
    b. first order
    c. second order
    d. third order
    e. fourth order
    a. zero order graph

          

  2. For the gas phase decomposition of ethyl chloroformate, ClCOOC2H5 → C2H5Cl + CO2
    The rate constant has been determined at several different temperatures. When the data is graphed as ln k vs. 1/T, the slope of the line is -1.48 x 104 and the y-intercept is 24.6.
    What is the activation energy, Ea, for this reaction?
    a. 9.62 kJ b. 15.0 kJ c. 123 kJ d. 205 kJ e. 1214 kJ
    b. 0.00648 M

          

  3. Which of the following expressions does not represent a proper expression for the rate of this reaction?
    2A + 3B → F + 2G

    a.
    b.
    c.
    d.
    e.


    ANS: A
    d. Their values get larger as the temperature is increased.

          

  4. The decomposition of dinitrogen pentoxide obeys the rate-law expression rate = 0.080 min−1[N2O5]. If the initial concentration of N2O5 is 0.30 M, what is the concentration after 2.6 minutes?
    N2O5 → N2O3 + O2

    a. 0.38 M
    b. 0.028 M
    c. 0.24 M
    d. 0.13 M
    e. 0.32 M
    c. 0.24 M

          

  5. One of the reactions that is used to produce gaseous hydrogen commercially follows. A proper expression for the rate of this reaction could be ____.
    H2O(g) + CO(g) → H2(g) + CO2(g)

    a.
    b.
    c. k
    d.
    e.
    -DH2O/Dt

          

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