Faraday Constant

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Faraday's Constant Number

The Faraday's constant number can be defined as the amount of electric charge which is being carried by one mole or as per Avogadro's number. Its relevance can be found across different subjects like Chemistry, Physics and electronics. In general, the Faraday constant is represented via the italic uppercase alphabet F and has a measuring unit is Coulombs per mole (Cmol⁻¹).

Conceptualized in honor of the 19th Century scientist, Michael Faraday, this value can be used to learn more about electrochemical reactions. The Faraday Constant’s value as figured out to be:

9.6485333289 × 10⁴ Cmol⁻¹ or 6.022140857 × 10²³ electrons.

Relationship Between Coulombs and Faraday Constant

In order to understand and define Faraday Constant, you must first need to understand Coulombs. The coulombs are generally recognized as the measure of the quantity of electricity, i.e., often represented in terms of amperes and seconds. 

1 Coulomb = Current (in amperes) × Time (in seconds)

An example for the same would be if a system has a flow of 5 amperes current in an hour, the total number of coulombs would be = 5 × 3600 (since an hour has 60 minutes; each minute having 60 seconds)

= 18000 coulombs. 

Electricity is the collectivity of the movement of electrons moving as a flow system. Since each electron carries a charge of 1.602176634 × 10⁻¹⁹ coulombs, 1 mole of electrons would comprise the charge by the value of the Avogadro's number:

 F = eNA (where F = Faraday’s Constant, NA = Avogadro’s Number, e = charge of a single electron)

F = 6.02214076 x 10²³ × 1.602176634 × 10⁻¹⁹ coulombs 

F = 96485.3321233100184 Cmol⁻¹.

There are many other units in which the Faraday constant can be expressed. These are: 

  • In 96485 Joules per volt gram

  • 23.061 kcal per volt gram

  • 26.801 A.h/mol.

Faraday Constant vs. Faraday Unit

The Faraday represents the unit electrical charge, which is equal to the magnitude of the charge in each mole of electrons. Therefore, the Faraday constant can be equivalent to just one Faraday, which is represented as lowercase f. 

Please note that the Faraday Constant shouldn't be mixed up with farad, which is represented as 1 farad = 1 coulomb per each volt. This serves as a unit of capacitance that has also been named after the English physicist, Michael Faraday. 

Relationship Between Faraday Constant and Faraday's Laws of Electrolysis

In 1833, before finding out the value of Avogadro's number, Michael Faraday found that in the process of electrolysis, the amount of charge F (Faraday Constant) that is required to deposit one mole of ions sharing the same valency on an electrode, be it anions on the anode or cations on the cathode; it always stays constant despite of the types of ions used. Therefore, it was because of Faraday Constant that the quantity of silver to be used in its electrolysis of cation Ag+ (that is to deposit in the electrode) was determined via this method.

Since the first law of Faraday states that for an electrochemical reaction of the substance having mass (m) gets deposited or released at the electrode is directly proportional to the amount of charge that is passed through it. Therefore, the mathematical equation of the process can be expressed as: 

m = Z . Q; where Q = charge in Coulombs, Z = proportionality expressed as gC⁻¹.

Therefore, the proportionality number can also be termed as the electrochemical equivalent (E) and defined as the mass-consumed at the electrodes per unit charge. Thus, Z can be represented as: 

\[Z = \frac{E}{96,845}\]

Since we already know that, 

Q = I.t (where I is the current in amperes, t is time in seconds)

Therefore, replacing it in the above equation yields:

\[m = \frac{E . I . t}{F} = \frac{M . I . t}{F . z}\]

where, M is the Molar mass of the substance in g mol⁻¹, I is the current in amperes, t is the time in seconds, F is the Faraday Constant, and z is the number of monovalent ions per substance. 

Faraday Constant and Boundary Condition Equations

Several equations can help understand the flux of ions of type via the Nernst-Planck equation:

\[j_{t} = -D \frac{dc_{i}}{dx} - \frac{ez_{i}c_{i}D}{k_{B}T} \frac{d\Psi}{dx}\]; where i = 1, 2  \[D_{1} = D_{2} = D, z_{1} = -z\]

Here, the scalar form of the account that is used for symmetry in the problem depends upon the electrode. Therefore, the concentrations can be measured in molm-3, while the difference between the electric current density can be measured with the help of the Faraday constant in the following formula, 

i = zF(j₁  - j₂), where j₁ and j₂ are salt adsorption or desorption in the electrode.

Even today, there are many ongoing pieces of research that aim to increase the accuracy of the Faraday constant.

FAQ (Frequently Asked Questions)

Q1. What are the Applications of Faraday Constant?

The Faraday constant is used widely across the fields of Chemistry, Physics, and Electronics. It is often used in several electrolysis processes, as it helps in learning the number of moles oxidized in the electrode. Apart from that, the Faraday constant is used across understanding the oxygen flow rate and charge transfers, fuel cells, and its equivalent enthalpy changes, etc.

Q2. How Much is one Coulomb?

One Coulomb can be represented by the abbreviation 'C' with its SI unit for the electric charge. The amount of one Coulomb can be likened to the amount of charge that passes from a current of one ampere one second, thus in figures, equal to the charge of 6.241 x 1018 protons.