Batteries used in alarm systems, flashlights, watches, calculators, audio systems, toys, radios, auto equipment, remote controls.
Batteries They are used to start car engines; they can also be used as temporary sources of electricity in places remote from populated areas.
Fuel cells used in the production of electrical energy (at power plants), emergency energy sources, autonomous power supply, transport, on-board power supply, mobile devices.
Electrolysis
Electrolysis- a physical and chemical process consisting of the release of electrodes constituents of dissolved substances or other substances resulting from secondary reactions at the electrodes, which occurs when an electric current passes through a solution or melt electrolyte.
The ordered movement of ions in conducting liquids occurs in an electric field that is created electrodes- conductors connected to the poles of the source electrical energy. Anode in electrolysis it is called the positive electrode, cathode- negative. Positive ions - cations- (metal ions, hydrogen ions, ammonium ions, etc.) - move towards the cathode, negative ions - anions- (ions of acid residues and hydroxyl group) - move towards the anode.
The phenomenon of electrolysis is widely used in modern industry. In particular, electrolysis is one of the methods for the industrial production of aluminum, hydrogen, as well as sodium hydroxide, chlorine, and organochlorine compounds [ source not specified 1854 days], manganese dioxide, hydrogen peroxide. A large number of metals are extracted from ores and processed using electrolysis (electroextraction, electrorefining). Also, electrolysis is the main process through which a chemical current source functions.
Electrolysis is used in wastewater treatment (electrocoagulation, electroextraction, electroflotation processes). It is used to produce many substances (metals, hydrogen, chlorine, etc.), when applying metal coatings (electroplating), and reproducing the shape of objects (electroplasty).
Faraday's first law
In 1832, Faraday established that the mass m of a substance released at the electrode is directly proportional to the electric charge q passing through the electrolyte: if it is passed through the electrolyte for a time t D.C. with current strength I. The coefficient of proportionality is called electrochemical equivalent of the substance. He is numerically equal to mass a substance released when a single electric charge passes through an electrolyte, and depends on the chemical nature of the substance.
Faraday's second law
Electrochemical equivalents various substances treat like them chemical equivalents.
Chemical equivalent and she called relation molar mass A and she to his valency z. Therefore the electrochemical equivalent
where F - Faraday's constant.
Faraday's second law is written as follows
where M(g/mol) is the molar mass of a given substance formed as a result of electrolysis; I(A) - the strength of the current passed through a substance or mixture of substances; delta t(c) - time during which electrolysis was carried out; F (C mol −1) - Faraday constant; n is the number of electrons participating in the process, which, at sufficiently large current values, is equal to the absolute value of the charge of the ion (and its counterion) directly involved in electrolysis (oxidized or reduced).
1. Faraday's first law is fundamental quantity law electrochemistry.
2.Electrochemical equivalent.
3.Coulometers.Classification of coulometers.
4. Exit of substance by current.
5. Methods for determining current output when using direct and pulsed current.
6.Faraday's second law.
7. Apparent cases of deviation from Faraday's laws.
1. Faraday's first law
There are three main types of coulometers: gravimetric (gravimetric), volumetric (volumetric) and titration.
In weighing coulometers (these include silver and copper), the amount of electricity passed through them is calculated by the change in the mass of the cathode or anode. In volumetric coulometers, the calculation is made based on measuring the volume of the resulting substances (gas in a hydrogen coulometer, liquid mercury in a mercury coulometer). In titration coulometers, the amount of electricity is determined from titration data of substances formed in solution as a result of an electrode reaction.
Copper coulometer most common in practice laboratory research, because it is easy to manufacture and quite accurate. The accuracy of determining the amount of electricity is 0.1%. The coulometer consists of two copper anodes and a thin copper foil cathode located between them. The electrolyte in a copper coulometer is an aqueous solution of the following composition: CuSO 4 ∙ 5H 2 O, H 2 SO 4 and ethanol C 2 H 5 OH. Sulfuric acid increases electrical conductivity electrolyte and, in addition, prevents the formation of basic copper compounds in the cathode space, which can be adsorbed on the cathode, thereby increasing its mass. H 2 SO 4 in the copper coulometer electrolyte is necessary to prevent the accumulation of Cu 1+ compounds that can form as a result of the disproportionation reaction:
Cu 0 + Cu 2+ → 2Cu +
Ethyl alcohol is added to the electrolyte to obtain more finely crystalline, compact cathode deposits and to prevent oxidation of the copper electrodes of the coulometer.
The amount of electricity passed is judged by the change in the mass of the cathode, before and after electrolysis.
cathode, and the anode is made of pure silver.
A neutral or slightly acidic 30% solution of silver nitrate is used as an electrolyte in a silver coulometer.
Gas hydrogen-oxygen coulometer used for approximate measurements of small amounts of electricity. It measures the total volume of hydrogen and oxygen released during electrolysis aqueous solution H 2 SO 4 or NaOH, and from this value the amount of electricity passed is calculated. These coulometers are used relatively rarely, because Their accuracy is low, and they are less convenient to use than weighing coulometers.
Volumetric coulometers also include mercury coulometer. It is mainly used in industry to measure the amount of electricity. The accuracy of a mercury coulometer is 1%, but it can operate at high densities current The anode is mercury. Coal is the cathode. The electrolyte is a solution of mercury iodide and potassium iodide. The amount of electricity is calculated from the level of mercury in the tube.
The most common of titration coulometers– iodine
And Kistyakovsky coulometer.
An iodine coulometer is a vessel with platinum-iridium electrodes separated by cathode and anode spaces. A concentrated solution of potassium iodide with the addition of of hydrochloric acid, into the cathode compartment - a solution of hydrochloric acid. When a current is passed through the anode, iodine is released, which is then titrated with sodium thiosulfate (Na 2 S 2 O 3). Based on the titration results, the amount of electricity is calculated.
Kistyakovsky coulometer- This is a glass vessel. The anode is a silver wire soldered into a glass tube with mercury to ensure contact. The vessel is filled with a solution of potassium nitrate (15-20%). A platinum-iridium cathode is immersed in this solution. When current is passed, anodic dissolution of silver occurs. And also based on the results of titration of the solution, the amount of electricity is calculated.
4. Current output
Zn 2+ +2ē →Zn
If several parallel electrochemical reactions occur on the electrode, then Faraday’s first law will be valid for each of them.
For practical purposes, in order to take into account what fraction of the current or amount of electricity passing through the electrochemical system is spent on each specific reaction, the concept output of a substance by current.
Thus, VT makes it possible to determine the part of the amount of electricity passed through the electrochemical system, which accounts for the share of this electrochemical reaction.
Knowledge of VT is necessary, as in solving theoretical issues: for example, when constructing partial polarization curves and elucidating the mechanism of an electrochemical reaction, and in the practice of electrodeposition of metals, non-metals, alloys, in order to assess the effectiveness of a technological operation. In practice, VT is most often determined by dividing the practical mass of a substance by the theoretical mass determined by Faraday’s law.
m practical – the mass of a substance practically transformed as a result of the passage of a certain amount of electricity; m theor is the mass of a substance that should theoretically transform when passing the same amount of electricity.
The VT for processes occurring at the cathode, as a rule, do not coincide with the VT of the anodic processes, therefore it is necessary to distinguish between the cathode and anode current output. Until now, we have considered cases of determining VT when a direct electric current flows through the interface between a conductor of the first type and a conductor of the second type.
5. Methods for determining VT using pulsed current
If, however, flows across the phase boundary pulse current, then when determining VT there arise great difficulties. There is no single method or instrument for determining VT during pulse electrolysis. The difficulty of determining VT under pulsed electrolysis conditions is due to the fact that the current passing through the system is spent not only on the electrochemical reaction, but also on charging the electrical double layer. Electricity, passing through the interface and causing an electrochemical transformation, is often called Faraday current. The charging current is spent on charging the electrical double layer, reorganizing the solvent, the reagent itself, i.e. everything that creates the conditions for an electrochemical reaction to occur, so the expression for the total current passing through the electrochemical system will be as follows:
I = Iz + Iph, where Iz is the charging current, Iph is the Faraday current.
If no definition is required absolute values VT, then as a criterion for assessing the efficiency of pulsed electrolysis, one can use the ratio of the amount of electricity spent on dissolving the precipitate to the amount of electricity spent on its formation.
6. Faraday's second law.
Mathematically, this law is expressed by the equation:
Faraday's second law is a direct consequence of the first law. Faraday's second law reflects the relationship that exists between the amount of reacted substance and its chemical nature.
According to Faraday's second law:
If at the interface between a conductor of the first kind and a conductor of the second kind one and only one electrochemical reaction occurs, in which several substances participate, then the masses of the participants in the reaction that have undergone transformations relate to each other as their chemical equivalents.
7. Apparent cases of deviation from Faraday's laws
Faraday's First Law, based on the atomic nature of matter and electricity, is an exact law of nature. There can be no deviations from it. If in practice deviations from this law are observed during calculations, they are always due to incomplete consideration of the processes accompanying the main electrochemical reaction. For example, during the electrolysis of an aqueous solution of NaCl in a system with platinum electrodes and anode and cathode spaces separated by a porous diaphragm, the following reaction occurs at the cathode:
2H 2 O + 2ē = H 2 + 2OH -
and at the anode: 2Cl - - 2ē = Cl 2
Quantity formed chlorine gas is always less than what follows according to Faraday’s law due to the fact that Cl 2 dissolves in the electrolyte and enters into a hydrolysis reaction:
Cl 2 + H 2 O → HCl+ HClO
If we take into account the mass of chlorine that reacted with water, we obtain a result corresponding to that calculated according to Faraday’s law.
Or, during the anodic dissolution of many metals, two processes occur in parallel - the formation of ions of normal valence and the so-called subions - i.e. ions of lower valence, for example: Cu 0 - 2ē → Cu 2+ and
Cu- 1ē → Cu +. Therefore, the calculation according to Faraday’s law under the assumption that only ions are formed highest valence turns out to be wrong.
Often, not one electrochemical reaction occurs at the electrode, but several independent parallel reactions. For example, when separating Zn from an acidic solution of ZnSO 4 along with the discharge of Zn ions:
Zn 2+ +2ē →Zn
the reduction reaction of hydronium ions occurs: 2H 3 O + +2ē → H 2 + 2H 2 O.
If several parallel electrochemical reactions occur on the electrode, then Faraday’s first law will be valid for each of them.
The emergence of electromotive force of induction was the most important discovery in the field of physics. It was fundamental for the development technical application this phenomenon.
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Michael Faraday
Story
In the 20s of the 19th century, the Dane Oersted observed the deflection of a magnetic needle when it was placed next to a conductor through which an electric current flowed.
Michael Faraday wanted to explore this phenomenon more closely. With great tenacity he pursued his goal of converting magnetism into electricity.
Faraday's first experiments brought him a number of failures, since he initially believed that a significant direct current in one circuit could generate a current in a nearby circuit, provided there was no electrical communication between them.
The researcher modified the experiments, and in 1831 they were crowned with success. Faraday's experiments began by winding copper wire around a paper tube and connecting its ends to a galvanometer. The scientist then placed a magnet inside the coil and noticed that the galvanometer needle gave an instantaneous deflection, indicating that a current had been induced in the coil. After removing the magnet, there was a deviation of the arrow in opposite direction. Soon, in the course of other experiments, he noticed that at the moment of applying and removing voltage from one coil, a current appeared in a nearby coil. Both coils had a common magnetic circuit.
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Faraday's experiments
Faraday's numerous experiments with other coils and magnets were continued, and the researcher found that the strength of the induced current depends on:
- number of turns in the coil;
- magnet strength;
- the speed at which the magnet was immersed in the coil.
The term electromagnetic induction (EMF) refers to the phenomenon that an emf is generated in a conductor by an alternating external magnetic field.
Formulation of the law of electromagnetic induction
Verbal formulation of the law electromagnetic induction: the induced electromotive force in any closed loop is equal to the negative time rate of change magnetic flux, enclosed in a chain.
This definition is expressed mathematically by the formula:
E = - ΔΦ/ Δt,
where Ф = B x S, with magnetic flux density B and area S, which is crossed perpendicularly by the magnetic flux.
Additional Information. There are two different approaches to induction. The first explains induction using the Lorentz force and its action on a moving electric charge. However, in certain situations such as magnetic shielding or unipolar induction, problems may arise in understanding physical process. The second theory uses the methods of field theory and explains the process of induction using variable magnetic fluxes and the associated densities of these fluxes.
The physical meaning of the law of electromagnetic induction is formulated in three provisions:
- A change in the external MF in a wire coil induces a voltage in it. When the conducting electrical circuit is closed, the induced current begins to circulate through the conductor;
- The magnitude of the induced voltage corresponds to the rate of change of the magnetic flux associated with the coil;
- The direction of the induced emf is always opposite to the cause that caused it.
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Law of Electromagnetic Induction
Important! The formula for the law of electromagnetic induction is applied in general case. There is no known form of induction that cannot be explained by a change in magnetic flux.
Induction emf in a conductor
To calculate the induction voltage in a conductor that moves in the MF, another formula is used:
E = - B x l x v x sin α, where:
- B – induction;
- l is the length of the conductor;
- v – speed of its movement;
- α is the angle formed by the direction of movement and vector direction magnetic induction.
Important! A way to determine where it is directed induced current, created in the conductor: placing right hand palm perpendicular to entry power lines MP and, assigned thumb indicating the direction of movement of the conductor, we recognize the direction of the current in it by the straightened four fingers.
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Right hand rule
Laws of electrolysis
Faraday's historical experiments in 1833 were also related to electrolysis. He took a test tube with two platinum electrodes immersed in dissolved tin chloride heated with an alcohol lamp. Chlorine was released on the positive electrode, and tin was released on the negative electrode. He then weighed the released tin.
In other experiments, the researcher connected containers with different electrolytes in series and measured the amount of substance deposited.
Based on these experiments, two laws of electrolysis are formulated:
- The first of them: the mass of the substance released at the electrode is directly proportional to the amount of electricity passed through the electrolyte. Mathematically it is written like this:
m = K x q, where K is a constant of proportionality, called the electrochemical equivalent.
Formulate its definition as the mass of a substance in g released at the electrode when a current of 1 A passes in 1 s or when 1 C of electricity passes;
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First law of electrolysis
- Faraday's Second Law states that if the same amount of electricity is passed through different electrolytes, then the amount of substances released at the corresponding electrodes is directly proportional to their chemical equivalent (the chemical equivalent of a metal is obtained by dividing its molar mass by its valency - M/z).
For the second law of electrolysis, the following notation is used:
HereF – Faraday's constant, which is determined by the charge of 1 mole of electrons:
F = Na (Avogadro's number) x e (elementary electric charge) = 96485 C/mol.
Write another expression for Faraday's second law:
m1/m2 = K1/K2.
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Second Law of Electrolysis
For example, if you take two electrolytic containers connected in series containing a solution of AgNO 3 and CuSO 4 and pass the same amount of electricity through them, then the ratio of the mass of deposited copper on the cathode of one container to the mass of deposited silver on the cathode of the other container will be equal to the ratio of their chemical equivalents. For copper it is Rate this article:
