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In a question that I came across they defined $1\,\pu{F}$ as 96500 coulomb per equivalent. Now as far as my knowledge is concerned $1\,\pu{F} = 96500\,\pu{C/mol}$. The question involved asks to calculate the current that needs to be passed (or may be a function of that) wherein I mistook the $n$ factor and the answer was just half of what it was supposed to be. However that taking $1\,\pu{F}$ as "coulomb per equivalent" would lead me to a antoher unit (equivalent per mole) in order to get the desired unit in the question.

In this context I would like to:

a) Get an intuitive explanation into the number of equivalents (just like moles is Avogadro number of substances).

b) Know what the unit "equivalents/mole" means (is it the same thing as $n$ factor?) How does the $n$ factor treat number of moles and equivalents so differently?

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  • $\begingroup$ This is one of the best and unanswered question that I have come across.I intend to give some reputation for a better answer to the question.How to do that?Kudos @Rajorshi Koyal. $\endgroup$
    – user586228
    Mar 23, 2020 at 5:55
  • $\begingroup$ I am unable to completely understand what you said here: "However that taking 1F as "Coulomb per equivalent" would lead me to a unit equivalent per mole in order to get the desired unit in the question." Can you please elaborate on this? $\endgroup$
    – Aumkaar Pranav
    Mar 23, 2020 at 6:35
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    $\begingroup$ There is confusion in the 1st sentence. 1F = 1V / 1 C is 1 Farad, the unit of electrostatic capacitance. F without a quantifier is Faraday's constant equal to the charge equivalent to a molar equivalent. I.e. to 1 mol, If 1 electron is exchanged, or to 1/n moles, if n electrons are exchanged. F = Na . e, the multiple of the Avogadro constant and the elementary charge. $\endgroup$
    – Poutnik
    Mar 23, 2020 at 7:12
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    $\begingroup$ In redox reaction, one equivalent of a substance is simply the number of moles of it that accepts or donates one mole of electrons. Notice how equivalent is not defined as an independent quantity like mole. One equivalent of electrons is simply one mole of electrons. $\endgroup$
    – Aumkaar Pranav
    Mar 23, 2020 at 7:27
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    $\begingroup$ Does this answer your question? What is an equivalent? $\endgroup$
    – Aumkaar Pranav
    Mar 23, 2020 at 10:57

1 Answer 1

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For an electrochemical reaction, you count the atoms / ions by mol, and use the coulomb as a counting unit of charge. For a more intuitive explaination of the $n$ factor in the Faraday equation, try this analogy:

The summer olympics include swimming in a pool with lanes $50\,\pu{m}$ long. Among the typical competitions are runs about $50$, and $100\,\pu{m}$. Now, for the sake of the analogy, think the swimmers were representatives of ions. Each of the swimmers could represent

  • a $\ce{Cl-}$ to yield $\ce{Cl}$, a change by one unit of charge. So they swimm only one lane in one competition, $n = 1$; the single discharge happens when the swimmers clap the wall with their hand.

  • a $\ce{Cu^{2+}}$ wanting to yield $\ce{Cu}$. As they start with two charges now, two discharges in this single race are required ($n = 2$). Their first discharge is when they contact and turn at the opposite wall ($50\,\pu{m}$), their second and final discharge when they clap the other wall with their hand ($100\,\pu{m}$).

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