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Temperature Dependence and Solvent Effects

Our examination of collision events led to the conclusion that the rate of two-body collisions has a second order dependence on the concentration(s) of the species (Equation 6.7). We realize that a two-body collision event corresponds to an elementary second order (bimolecular) process, and hence, the rate law for a bimolecular process has the same second order dependence on concentration. A complete gas kinetic analysis of collisions requires that we recognize that molecules in a gas have a distribution of velocities. Since this distribution is prescribed by the temperature, we can ask what happens when the temperature is changed. [Pg.142]

The factor of is introduced so that the rate is in terms of moles rather than molecules. Notice [Pg.142]

an important feature is that the rate constant, k , varies with temperature. [Pg.142]

Laboratory determination of an exponential dependence of reaction rate constants on temperature was accomplished over 100 years ago by Svante Arrhenius (Sweden, 1859-1927). His work provided an expression that can be applied in studying most chemical reactions. [Pg.142]

E i stands for the activation energy which is the molar equivalent of the barrier height designated Vab in this discussion. The value A in Equation 6.40 is sometimes called a frequency or pre-exponential factor. It is somewhat dependent on temperature, var3dng as /T in the hard-sphere picture because of the collision rate s dependence on temperature. This factor can often be approximated as a constant over limited ranges of temperature. [Pg.142]


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