The units of rate constants in chemical kinetics
The units of rate constants in chemical kinetics
This short article discusses the units of rate constants as used in chemical kinetics and, in particular, the aspect of non-integral powers of base units, which some might find unusual for units in the SI system. In many ways the fact that the units of the rate constants as usually defined convey information about the order of the reaction or reactions involved is very useful, but in other ways having the same (or at least very similar) quantity that has different units under different conditions is not so desirable. Furthermore, just as with chemical equilibrium constants, taking functions of the rate constant (such as the logarithm when representing the Arrhenius equation in the form ln kvs.1/T) needs special attention. Here we examine a possible alternative definition of rate constants in terms of an explicit ratio to the concentration standard state and although we acknowledge that this approach unlikely to be adopted by the community, it serves as a basis to discuss the meaning of rate constants.
Chemical kinetics, Dimensions, Rate constants, Units
Frey, Jeremy G.
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Wallington, T.J.
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Hartshorn, Richard
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Quack, Martin
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Heus, Pascal
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Emmerson, Steven
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Frey, Jeremy G.
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Wallington, T.J.
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Hartshorn, Richard
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Quack, Martin
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Heus, Pascal
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Emmerson, Steven
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Frey, Jeremy G., Wallington, T.J., Hartshorn, Richard, Quack, Martin, Heus, Pascal and Emmerson, Steven
(2022)
The units of rate constants in chemical kinetics.
Accreditation and Quality Assurance, 2022 (10).
(doi:10.1007/s00769-022-01515-w).
Abstract
This short article discusses the units of rate constants as used in chemical kinetics and, in particular, the aspect of non-integral powers of base units, which some might find unusual for units in the SI system. In many ways the fact that the units of the rate constants as usually defined convey information about the order of the reaction or reactions involved is very useful, but in other ways having the same (or at least very similar) quantity that has different units under different conditions is not so desirable. Furthermore, just as with chemical equilibrium constants, taking functions of the rate constant (such as the logarithm when representing the Arrhenius equation in the form ln kvs.1/T) needs special attention. Here we examine a possible alternative definition of rate constants in terms of an explicit ratio to the concentration standard state and although we acknowledge that this approach unlikely to be adopted by the community, it serves as a basis to discuss the meaning of rate constants.
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Accepted/In Press date: 19 June 2022
e-pub ahead of print date: 11 October 2022
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© 2022, The Author(s).
Keywords:
Chemical kinetics, Dimensions, Rate constants, Units
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Local EPrints ID: 476212
URI: http://eprints.soton.ac.uk/id/eprint/476212
ISSN: 0949-1775
PURE UUID: cf3f8125-a735-427e-b0ad-e81482f3d2e6
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Date deposited: 14 Apr 2023 16:38
Last modified: 17 Mar 2024 02:33
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Author:
T.J. Wallington
Author:
Richard Hartshorn
Author:
Martin Quack
Author:
Pascal Heus
Author:
Steven Emmerson
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