Temperature Dependence of Rate Constants Activation Energies

Temperature Dependence of Rate Constants Activation Energies 

The rates of chemical reactions are very sensitive to temperature changes. For example, it is a very rough empirical rule that reactions double their speed with an increase in temperature of 10 C (at 300 K). This means that whereas for the first-order process an increase in the concentration of 100 per cent is required to double the specific rate, the same effect can be achieved by a 10 C increase in temperature. 

The first quantitative, experimental formulation of the dependence of reaction rates on temperature was made by Hood and later extended by Arrhenius. The form of the dependence of the specific rate constant on temperature is 

which is known as the Arrhenius equation, k is the specific rate constant at some temperature, T is the absolute temperature, R is the gas constant, and A and E are empirical constants. 

It is found experimentally that such an equation does indeed provide a reasonably accurate description of the temperature dependence of specific rate constants over a fairly wide temperature range and for constants representing reactions of different orders. Experimentally the constants A and E may be determined from a plot of the logarithm of the specific rate constant k against the reciprocal of the absolute temperature. Such a plot is shown in Fig. IV.3. (The use of these coordinates allows the data to be presented in the form of a straight line.) 

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Temperature-dependence of rate constants activation energy and entropy... 

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