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2013-11-22T16:37:00Z

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In [[cyclic voltammetry]], the '''Randles–Sevcik equation''' describes the effect of scan rate on the peak current ''ip''. For simple redox events such as the [[ferrocene]]/[[ferrocenium]] couple, ''ip'' depends not only on the concentration and diffusional properties of the electroactive species but also on scan rate.<ref>P. Zanello, "Inorganic Electrochemistry: Theory, Practice and Application" The Royal Society of Chemistry 2003. ISBN 0-85404-661-5</ref>

<math>i_p = 0.4463 \ nFAC \left(\frac{nFvD}{RT}\right)^{\frac{1}{2}}</math>

Or if the solution is at room temperature:

<math>i_p = 268,600 \ n^{\frac{3}{2}} AD^{\frac{1}{2}} Cv^{\frac{1}{2}} </math>

*''ip'' = current maximum in amps
*''n'' = number of electrons transferred in the redox event (usually 1)
*''A'' = electrode area in cm2
*''F'' = The [[Faraday constant|Faraday Constant]] in C mol−1
*''D'' = diffusion coefficient in cm2/s
*''C'' = concentration in mol/cm3
*''ν'' = scan rate in V/s
For novices in electrochemistry, the predictions of this equation appear counter-intuitive, i.e. that ''ip'' increases at faster voltage scan rates. It is important to remember that current, i, is charge (or electrons passed) per unit time. Therefore, at faster voltage scan rates the charge passed per unit time is greater, hence an increase in ip, while the total amount of charge is the same.

==Uses==
Using the relationships defined by this equation, the [[diffusion coefficient]] of the electroactive species can be determined. Linear plots of ''ip'' vs. ''ν''1/2 provide evidence for a chemically reversible redox process vs the cases where redox causes major structural change in the analyte. For species where the diffusion coefficient is known (or can be estimated), the slope of the plot of ''ip'' vs. ''ν''1/2 provides information into the stoichiometry of the redox process.

==References==
<references/>

==See also==
*On-line calculator for use of Randles–Sevcik equation:http://www.calctool.org/CALC/chem/electrochem/cv1

{{DEFAULTSORT:Randles-Sevcik equation}}
[[Category:Electrochemical equations]]

Relative growth rate - Revision history

en>Smartse: add missing 'time'