The first and second law of Faraday

Electrolyte always has a certain number of ions with plus and minus signs, resulting from the interaction of molecules of the dissolved substance with the solvent. When an electric field appears in it, the ions begin to move toward the electrodes, the positive ones turn to the cathode, the negative ones to the anode. Having reached the electrodes, ions give them their charges, turn into neutral atoms and deposited on the electrodes. The more ions approach the electrodes, the more matter will be deposited on them.

We can come to this conclusion by experience. Let's pass the current through an aqueous solution of copper sulfate and observe the release of copper on the carbon cathode. We find that at first it will cover with a barely noticeable layer of copper, then as it passes through the current it will increase, and if the current is transmitted for a long time, a copper layer can be obtained on a carbon electrode of considerable thickness, to which it is easy to solder, for example, a copper wire.

The phenomenon of the release of matter on the electrodes during the passage of current through the electrolyte is called electrolysis.

Passing through different electrolyses various currents and carefully measuring the mass of matter released on electrodes from each electrolyte, the English physicist Faraday in 1833 - 1834 gg. Discovered two laws for electrolysis.

The first law of Faraday establishes the relationship between the mass of the released substance during electrolysis and the amount of charge that passed through the electrolyte.

This law is formulated as follows: the mass of matter that was released during electrolysis on each electrode is directly proportional to the magnitude of the charge that passed through the electrolyte:

M = kq,

Where m is the mass of the substance that was released, q is the charge.

The value of k is the electrochemical equivalent of the substance. It is characteristic for each substance released during electrolyte.

If the formula takes q = 1 as a coulomb, then k = m, i.e. The electrochemical equivalent of the substance will be numerically equal to the mass of the substance separated from the electrolyte upon passage of the charge into one pendant.

Expressing in the formula the charge through the current I and the time t, we get:

M = kIt.

The first Faraday law is verified experimentally as follows. Let's pass current through electrolytes A, B and C. If they are all the same, then the masses of the separated substance in A, B and C will be referred to as currents I, I1, I2. In this case, the amount of matter extracted in A will be equal to the sum of the volumes allocated in B and C, since the current I = I1 + I2.

The second law of Faraday establishes the dependence of the electrochemical equivalent on the atomic weight of the substance and its valence and is formulated as follows: the electrochemical equivalent of the substance will be proportional to their atomic weight, and also inversely proportional to its valence.

The ratio of the atomic weight of a substance to its valence is called the chemical equivalent of a substance. Having introduced this value, Faraday's second law can be formulated differently: the electrochemical equivalents of the substance are proportional to their own chemical equivalents.

Let the electrochemical equivalents of different substances be equal, respectively, to k1 and k2, k3, ..., kn, the chemical equivalents of the same substances x1 and x2, x23, ..., xn, then k1 / k2 = x1 / x2, or k1 / x1 = k2 / x2 = K3 / x3 = ... = kn / xn.

In other words, the ratio of the magnitude of the electrochemical equivalent of a substance to the value of the same substance is a constant value, having for all substances the same value:

K / x = c.

It follows that the ratio k / x is constant for all substances:

K / x = c = 0, 01036 (mg-eq) / k.

The value of c shows how many milligram equivalents of the substance is released on the electrodes during passage through the electrolyte of the electric charge, equal to 1 pendant. The second Faraday law is represented by the formula:

K = cx.

Substituting the obtained expression for k into Faraday's first law, both can be combined in one expression:

M = kq = cxq = cxIt,

Where c is the universal constant, equal to 0, 00001036 (g-eqv) / k.

This formula shows that, by passing the same currents for the same time interval through two different electrolytes, we will separate from both electrolytes the quantities of substances that are related to the chemical equivalents of such electrolytes.

Since x = A / n, we can write:

M = cA / nIt,

That is, the mass of matter released on electrodes during electrolysis will be directly proportional to its atomic weight, current, time, and inversely proportional to its valence.

The second Faraday law for electrolysis, just like the first, directly follows from the ionic nature of the current in the solution.

The law of Faraday, Lenz, and many other outstanding physicists played a huge role in the history of the formation and development of physics.