Plot of ln k vs 1/T

The first line of input should be the name of the time units (e.g, hours), followed by a comma and the number of seconds per time unit (e.g., 3600 for hours). On separate lines, enter the temperature (in Celsius) and the associated rate constant, separated by commas, spaces or tabs. Entering the time units is only important if you are interested in the activation entropy; it has no bearing on the activation energy.

Press the calculate button. The routine fits the data to the

The pre-exponential factor,

An equation is provided that allows the reaction rate constant to be calculated at a specified temperature. From the reaction rate constant, the concentration may be calculated assuming a first-order decrease with time.

The Arrhenius calculation assumes that the pre-exponential factor,

As a check the difference between the activation energy and enthalpy should be equal to RT.

For first-order reactions, the units of the rate constants should be in terms of inverse time. For second-order reactions, the units of the rate constants should be in terms of inverse molarity-time in order for the calculations to work out.

An example is given from The Physical Basis of Organic Chemistry by Howard Maskill (1990 edition), p. 232, using data from GR Brandon et al.,

seconds, 1

235.6, 0.0000376

244, 0.0000763

248.4, 0.000108

252.9, 0.000153

256, 0.000193

259.3, 0.000244

262.4, 0.000332

267.2, 0.000461

278.7, 0.00105

285, 0.00166

The calculated activation energy is 181 kJ/mol, the activation entropy is 12.4 J/K.mol, and the activation enthalpy is 176 kJ/mol.

Thanks to Professor Richard L Schowen for pointing out an error in an earlier version of this page. Of course, any mistakes in the current version are strictly my own responsibility.

Jeffrey Clymer -- Debut: April 13, 1997. Revision 8: December 30, 2015 -- Email -- Homepage

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