Chapter 15: Q88 E (page 647)
The activation energy for the reaction
is for the reaction is . What is the activation energy for the reverse reaction ?
The activation energy for the reverse reaction is .
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The thermal degradation of silk was studied by Kuruppillai, Hersh, and Tucker (“Historic Textile and Paper Materials,”ACS Advances in Chemistry Series, No. 212, 1986) by measuring the tensile strength of silk fibres at various time of exposures to elevated temperature. The loss of tensile strength follows first-order kinetics,
Where s is the strength to the fibre retained after heating and k is the first-order rate constant. The effects of adding a deacidifying agent and an antioxidant to the silk were studied, and the following data were obtained:
a. Determine the first-order rate constants for thermal degradation of silk for each of the three experiments
b. Does either of the two additives appear to retard the degradation of silk?
c. Calculate the half-life for the thermal degradation of silk for each of the three experiments.
Assuming that the mechanism for the hydrogenation ofC2H4 given in Section 15.9 is correct, would you predictthat the product of the reaction of C2H4 with D2 wouldbe CH2D-CH2D or CHD2-CH3?
The decomposition of Hydrogen Iodide on finely divided gold atis zero order with respect to HI. The rate defined below is constant at .
(a) If the initial HIconcentration was, calculate the concentration ofHI at 25minutes after the start of the reaction.
(b) How long will it take for all of the 0.250 MHIto decompose?
Consider the hypothetical reaction
which is assumed to occur by the mechanism
where represents a molecule with enough energy to surmount the reaction energy barrier.
(a) Derive the rate law for the production of using the steady-state approximation.
(b) Assume that this condition is known to be first order. Under what conditions does your derived rate law (from part a) agree with this observation.
(c) Explain how a chemical reaction can be first order, since even in a simple case molecules must collide to build up enough energy to get over the energy barrier. Why aren’t all reactions at least second order ? In other words, explain the physical significance of the result from part b.
What are the units for each of the following if concentrations are expressed in moles per litre and time in seconds?
a. Rate of a chemical reaction
b. Rate constant for a zero-order rate law
c. Rate constant for a first-order rate law
d. Rate constant for a second-order rate law
e. Rate constant for a third-order rate law
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