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An Arrhenius plot displays the logarithm of a rate (ln(k), ordinate axis) plotted against inverse temperature (1 / T, abscissa). Arrhenius plots are often used to analyze the effect of temperature on the rates of chemical reactions. For a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined.
| Example: Nitrogen dioxide decay |
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k against T |
ln(k) against 1/T |
The Arrhenius equation given in the form:
can be written equivalently as:
- Where:
- k = Rate constant
- A = Pre-exponential factor
- Ea = Activation energy
- R = Gas constant
- T = Absolute temperature, K
- Where:
When plotted in the manner described above, the value of the extrapolated "y-intercept" will correspond to ln(A), and the gradient of the line will be equal to − Ea / R.
The pre-exponential factor, A, is a constant of proportionality that takes into account a number of factors such as the frequency of collision between and the orientation of the reacting particles.
The expression − Ea / RT represents the fraction of the molecules present in a gas which have energies equal to or in excess of activation energy at a particular temperature.
See also
Wikipedia content modification information:
- This page was last modified on 21 October 2008, at 21:26.
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