The theory of absolute reaction rates is developed for condensed phases. The equation for the rate of a reaction of any order in any phase where the slow process is the passage over an energy barrier consists of the product of a transmission coefficient κ, a frequency kT/h, an equilibrium constant between an activated complex and the reactants and an activity coefficient factor. Previous theories of reaction rates such as Brönsted's, the collision theory of Mc C. Lewis, etc., are seen to be special cases of the general theory. A variety of examples are considered.
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This equation applies only up to pressures of a few atmospheres. At the critical point α is of course unity. A more exact equation would take account of the decrease in the temperature dependence of α by including terms in the denominator of the general form
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For a bimolecular reaction at about 50–100 °C a kinetic theory collision diameter of 2A is equivalent to an entropy of activation of 6.9 while a diameter of 3A corresponds to 5.3 entropy units.
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Moelwyn‐Hughes, Kinetics of Reactions in Solution (1933), p. 79.
a Even for a “normal” reaction the rate in solution is greater by the activity factor Part of this factor is reflected in a smaller absolute value of the entropy of activation.
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© 1935 American Institute of Physics.
1935
American Institute of Physics
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