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In electrochemistry, the Nernst equation is a chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or full cell reaction) from the standard electrode potential, absolute temperature, the number of electrons involved in the redox reaction, and activities (often approximated by concentrations) of the chemical species undergoing ...
In aqueous solutions, redox potential is a measure of the tendency of the solution to either gain or lose electrons in a reaction. A solution with a higher (more positive) reduction potential than some other molecule will have a tendency to gain electrons from this molecule (i.e. to be reduced by oxidizing this other molecule) and a solution with a lower (more negative) reduction potential ...
The formal standard reduction potential ′ can be defined as the measured reduction potential of the half-reaction at unity concentration ratio of the oxidized and reduced species (i.e., when C red / C ox = 1) under given conditions. [3] Indeed:
The larger the value of the standard reduction potential, the easier it is for the element to be reduced (gain electrons); in other words, they are better oxidizing agents. For example, F 2 has a standard reduction potential of +2.87 V and Li + has −3.05 V: F 2 (g) + 2 e − ⇌ 2 F − = +2.87 V Li + + e − ⇌ Li (s) = −3.05 V
Reaction 1 is discarded as it has the most negative value on standard reduction potential thus making it less thermodynamically favorable in the process. When comparing the reduction potentials in reactions 2 and 4, the oxidation of chloride ion is favored over oxidation of water, thus chlorine gas is produced at the anode and not oxygen gas.
At a certain voltage E e, equilibrium will attain and the forward and backward rates (v f and v b) will be equal. This is represented by the green curve in the above figure. The equilibrium rate constants will be written as k fe and k be, and the equilibrium concentrations will be written c oe and c re.
For example, from Fe 2+ + 2 e − ⇌ Fe(s) (–0.44 V), the energy to form one neutral atom of Fe(s) from one Fe 2+ ion and two electrons is 2 × 0.44 eV = 0.88 eV, or 84 907 J/(mol e −). That value is also the standard formation energy (∆ G f °) for an Fe 2+ ion, since e − and Fe( s ) both have zero formation energy.
CV can also be used to determine the electron stoichiometry of a system, the diffusion coefficient of an analyte, and the formal reduction potential of an analyte, which can be used as an identification tool. In addition, because concentration is proportional to current in a reversible, Nernstian system, the concentration of an unknown solution ...