Straight ahead of the oxide-water reactions. Possibility and direct flow of ovr Possibility of oxide-water reactions

The understanding of the electrode potential does not suffice until the bet Me n + | Me pro, ale and before the system oxidized form | updated form. Yogo is called an oxidizing potential. Oxide-water potential, vymіryanyy for standard minds, is called the standard oxide-water potential. In electrochemistry, it is accepted that all the electrodes are equal to write directly to the process of renewal, so that the electrons are received:

Zn 2+ + 2e - \u003d Zn, E pro \u003d - 0.76 V

The values of the standard oxidation-water potentials of the plants in the final tables and are victorious for thermodynamic analysis of the possibility of OVR in water sources.

Mimovilni reactions are characterized by a negative value of the Gibbs energy ∆G o 298 . The Gibbs energy of the oxidative-reddening reaction can be expressed as a robot of an electric strum, which is in the galvanic cell, and can be connected with the EPC element. Tsey zv'yazok for standard minds

de D G 0 - standard Gibbs energy of the reaction, J; z- the number of moles of electrons that go from oxidizing agent to the oxidizing agent in this reaction, mole (it is the least significant multiple of the accepted and accepted electrons); F- Fast Faraday, rіvna 96484 C / mol; D E 0 - standard EPC of a galvanic cell, which is based on the reaction, Art.

D value E 0 are calculated through the standard potentials of the oxidizing reaction, and in addition to the potential of the oxidizing agent, it is necessary to take into account the potential of the oxidizer:

The values of the standard potentials for the reaction of oxidation and renewal can be used to calculate the constants of the equal reactions, depending on the onset of the reaction:

Stars can show the constant of the equal reaction K equal:

After the substitution of the rest of the post Fі R, as well as the standard temperature of 298 K (the scales of the values of the standard potentials are induced at the standard temperature) and after the transition from the natural logarithm to the tenth virase for the constant of the equalness of the oncoming look:

The Gibbs energy of the reaction serves as a sign of the thermodynamic possibility of the reactions and the establishment of a direct flow of the reverse reactions. reaction thermodynamically possible, otherwise it leaks angry to the right, like

reaction thermodynamically impossible, otherwise it leaks to the right, like

butt. Consider the possibility of oxidation in standard concentrations of hydrochloric acid and potassium bichromate. Verify the standard Gibbs energy and equal reaction constants with the help of a surveyor.

Solution. Record the equal oxidation-oxidation reaction and add up the oxidation reaction and renewal:

The value of the standard potentials for the reaction of inspiration () and oxidation () is taken from the table. 4 at the addendum. Countable D E 0:

We use the Gibbs energy of the reaction according to the formula ∆G o 298 = – z∙F∙∆E o . The number of moles of electrons, as it passes from an oxidizing agent to a hydrogen, depends on the stoichiometric coefficients of the equal reaction. The reaction takes part in 1 mol of K 2 Cr 2 O 7, which accepts 6 electrons in 6 ions Cl - . To that in my reaction z= 6. Gibbs energy of the reaction in standard minds is more expensive

We assign the equalization constant:

For reaction D G 0 > 0 and K rivn< 1, следовательно, реакция термодинамически невозможна в стандартных условиях.

CORROSION OF METALS

Corrosion of metals- The process of destruction of metals proceeds mimicively as a result of chemical and electrochemical interactions with the superfluous medium.

Chemical corrosion combined with metal and dry gases (O 2 , SO 2 , H 2 S lean) and rare non-electrolytes (oil, naphtha, gas).

4Ag + 2H 2 S + O 2 \u003d 2Ag 2 S + 2H 2 O

The reaction is explained by the darkening of the average vibrations again.

Electrochemical corrosion it occurs when metals are in contact with electrolits under the influx of galvanic couples, which are blamed (corrosive galvanic couples). With electrochemical corrosion, two processes occur simultaneously:

1) anodic process (metal oxidation)

Me pro - ne - \u003d Me n +

2) cathodic process (innovation of oxidizer)

O 2 + 2H 2 O + 4e - \u003d 4OH - (as an oxidizer - kisen)

2H + + 2e - \u003d H 2 (as an oxidizing acid - acid)

Sour corrosion occurs in neutral and basic varieties, and water corrosion occurs in acidic varieties.

butt. Let's look at the process of electrochemical corrosion of galvanized and nickel-plated fairings in a watery surface (neutral medium) and in hydrochloric acid, is the coating damaged?

Solution. Depending on the position of metals in a number of standard electrode potentials, it is known that zinc is the most active metal ( B), lower closed ( B), and in a corrosive galvanic pair, which is established, zinc will be the anode, and zinc will be the cathode. The zinc anode is different.

Anode process:

Zn – 2e – = Zn 2+

Electricity from zinc should be switched to cold, and between cold - electrolyte will be oxidized.

cathodic process:

2H + + 2e - \u003d H 2 (sour middle)

The product of corrosion in an acidic medium is the strength of ZnCl 2 in a neutral medium - hydroxide Zn (OH) 2:

Zn + 2НCl \u003d ZnCl 2 + H 2

2Zn + O 2 + 2H 2 O \u003d 2Zn (OH) 2

In this way, zinc (anodne) coating protects the hall from corrosion.

In the pair Fe - Ni, the active metal is free ( B), it acts as an anode and knows the ruin.

Anode process:

Fe - 2e - \u003d Fe 2+

cathodic process:

2H + + 2e - \u003d H 2 (sour middle)

O 2 + 2H 2 O + 4e - \u003d 4OH - (neutral medium)

The product of corrosion in an acidic medium is FeCl 2, and in a neutral one - Fe (OH) 2, which, in the presence of acid in electrolyte, is oxidized:

Fe + 2НCl \u003d FeCl 2 + H 2

2Fe + O 2 + 2H 2 O \u003d 2Fe (OH) 2

With whom, fluffy balls of brown iris are settled.

Covering the hall with less active metals (cathode cover) is effective, docks are damaged.

Chemically clean metal resistant to corrosion, low metal.

butt. What calls for corrosion to chavun?

Solution. Chavun may be a heterogeneous warehouse. Chavun is an alloy of saline with coal, with grains replaced by cementite Fe 3 C. Mіzh vіlnym metal and yogo with a semi-cooked galvanic couple. The anode at the same time was metal, and the cathode - cementite grains; For obviousness, salt (anode) begins to turn into Fe 2+ ions, which give with OH ions, which have settled on the grains of cementite (cathode), salt hydroxide (II), which oxidizes with sour to irzh.

Anode process:

Fe - 2e - \u003d Fe 2+

cathodic process:

O 2 + 2H 2 O + 4e - \u003d 4OH -

4Fe(OH) 2 + O 2 + 2H 2 O = 4Fe(OH) 3

Similar information.

In skin oxidative-oxidative reactions, including reactions

Zn + CuSO 4 \u003d ZnSO 4 + Cu (1)

take part in two oxidizing-redundant pairs - a vial (Zn) and another oxidized form (Zn 2+); oxidizing (Cu 2+) is the same form (Cu). To the world of oxidizing and expansive building given bet є oxidizing and proving or electrical potential, which means, de Ox - the oxidized form, Red - the renewed form (for example, , ). It is not possible to underestimate the absolute value of the potential, so it is necessary to subdue the standard, for example, a standard water electrode.

Standard aqueous electrode It is made up of a platinum plate covered with a thin powder of platinum, laced with sulfuric acid with a concentration of ions in water, which is 1 mol / l. Wash the electrode with a jet of gas-like water under a pressure of 1013 10 5 Pa at a temperature of 298 K. On the surface of the platinum, a reverse reaction occurs, as you can imagine:

2H + + 2 H 2 .

The potential of such an electrode take for zero: (potential expansion - Volt).

The standard potentials of vimiryans or insurance for a large number of oxide-drying pairs (navreaktsiy) and are indicated in the tables. For example, . Chim more value, more strong oxidizingє oxidized form (Оx) цієї pari. Chim less value of potential, more a strong guideє the form (Red) of the oxide-red bet has been renewed.

A number of metals, mixed in order to increase their standard electrode potentials, are called electrochemical series of metal voltages (number of metal activity):

Li Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd Co Ni Sn Pb H Bi Cu Ag Hg Au

E0< 0 E 0 =0 E 0 > 0

A series starts with the most active metals (powder), and ends with "noble" ones. important oxidizing metals. With the more powerful roztashovan in a row of metal, with the strongest influencing authorities, the stink of power, the stink can be removed from the rozchiniv salts, to stand right. Metals, roztashovanі to water, vitіsnyatіt yogo іz razchinіv acids (crim HNO 3 і H 2 SO 4 conc).

In quiet moods, if the system is known in non-standard minds, it appears

de - potential of the system for non-standard minds, V;

– system potential for standard minds, V;

R – universal gas steel (8.31 J/mol K);

T—temperature, K;

n is the number of electrons that the process has;

F is the Faraday number (96500 K/mol);

A, c – additional concentrations (mol/l) of oxidized and derived forms of participants in the process, at the levels of stoichiometric coefficients.

The concentration of solid speech and water is taken as one.

At a temperature of 298 K, after substituting the numerical values of R and F,

Nernst's equal looks at the sight:

. (2)

So, for napіvreaktsії

river Nernst

The vicorist value of the electrode potentials can be directly related to the mimic overshoot of the oxidation-oxidation reaction. In the course of the OVR, the electronics are constantly shifting in the form of a wager, to avenge the wind, to a wager, to avenge the oxidizing agent. Significantly

Electrodniy betting potential to avenge oxide;

To establish the possibility of mimicry in standard OVR minds, EPC, you can speed up the values of ΔG 0 298 for the reaction. The negative value of ΔG 0298 is the same as the positive value of EPC, to speak about those that in standard minds at 298 K, the reaction can proceed miraculously, without adding energy to the call.

In the case of a reverse change of the OVR in the minds p = const і V = const the change in the energy of Gibbs is more efficient for the electric robot Ael., which is created by the system.

∆G 0 = - Ael.

The potential of the OB bet is calculated for Nerist’s peers, as you can see

E \u003d E 0 + 0.059 a oxidized.

N lg a visible.

EPC = E 0 oxid. - E 0 visible. ; 3 twist / Z prod. = 1/K

At the level of equal activity of the reagents and products, the equal value of the EPC will become equal to zero, and the virus will be sign of the logarithm 1/K, then ln1/K = ln1 - lnK; ln1=0

O = ∆E 0 +(R T/n F) ln

ΔЕ 0 - (R T/n F) lnK

or +n ∙ F Δ E 0 = RT lnK

- n F ΔE 0 = ΔG

Vidpovidno to the II law of thermodynamics, they pass only processes that can Δ G<0, то реакция ОВР идет слева направо, только если ЭДС>0.

∆Gp = -RT lnK = -nF ∆E 0

As a strong oxide interacts with a strong agent, there is a one-way process. Vіn mayzhe leaks residually, tk. yogo products sound є from the floor zі weakly expressed by the oxidizing-authoritative powers. With low water content, the oxide-water activity of the outer speeches and products of the reaction is a two-sided process. For a calculus assessment of the directness of the processes, the values of G 0 reagents and products of the reaction are corrosive, and for the okremnaya drop of the OVR, which occurs in dilutions of water at t \u003d 25 0 C, 101 kPa, it can be estimated by the values of normal electrode potentials.

By setting the electrode potentials of different systems, it is possible to determine directly from any OVR proticatim.

Standard e.r.s. E 0 of the galvanic element is connected with the standard energy of Gibbs G 0 flows in the element of the reaction to spivvіdshnennia.

∆G 0 =-nF ∆E 0

On the other side, ∆G 0 is related to the equalization constant Before the reaction equals.

n F ΔE 0 = 2.3 RT lgK

lgK = n F Δ E 0 / 2.3 RT

lgK = n ∙ ΔE 0 / 0.059

Q can be given to the robot as the number of changes in the hour of the electric process nF (n is the number of electrons that can be transferred from the oxygen to the oxidizing agent in the elementary act of the reaction, F is the constant Faraday), multiplied by the difference in potentials E between the galvanic electrode.

ΔG= - n F ΔE

For OVR at T = 298 ΔG 0 = - n F ΔE 0

For the minds that are considered standard, for the system

Ox + ne↔Red The electrical potential is attributed to Nernst's equals

E o x / Red \u003d E 0 0 x / Red - (RT / n F) ln (C (Red) / C (Ox))

E ox / Red and E 0 ox / Red - electrode and standard potential of the system.

n is the number of electrons that the process has.

C(Red) and C ox molar concentrations of inspired and oxidized forms.

E ox / Red \u003d E 0 ox / Red - (0.059 / n) lg C (Red) / C (Ox)

For example:

for the MnO 4 - + 8H + + 5e ↔ Mn 2+ + 4H 2 O system

E MnO - 4 / Mn 2+ \u003d 1.51 - (0.059 / 5) lg (C Mn 2+ / C MnO - 4 C (H +) 8)

Select potassium halide as a guide for FeCl 3

2KG - + 2 Fe 3+ Cl 3 (P) = G 0 2 + 2KCl (P) + 2 Fe 2+ Cl 2 (P)

(G \u003d F -, Cl -, Br -, I -)

Behind the table: E 0 Fe 3+ / Fe +2 \u003d + 0.77B

E 0 F2/2F- = + 2.86B

E 0 Cl2/2Cl- = + 1.36B

E 0 Br2/2Br- = +1.07B

E 0 I 2/2 I - = +0.54B< 0.77 B

We can calculate the f.f.s. for the participation of hologenides for KI

ΔE 0298 \u003d E 0 oxid. - E 0 visible. \u003d 0.77 - 0.54 \u003d 0.23V\u003e 0. Only potassium iodide will be

changing the energy of the Gibbs reaction

ΔGreactions = ∑ΔG0298f(kіnevі) - ∑ΔG0298f(holidays)

On the application of the reaction 2NaOH + H2SO4 = Na2SO4 + H2O

Energy of Gibbs to illumine

ΔGreaction=[ΔGNa2SO4+ΔGH2O] - [ΔGH2SO4+ΔGNaOH*2]

The galvanic element is widely used in telephones, toys, signaling systems and others. Oskіlki a range of accessories, in which dry elements are vicarious, even wide and, moreover, they require periodic replacement

Electrolysis - the sequence of processes that take place on the electrodes during the passage of an electric stream through the design and melting of the electrolyte. Electrolytes are conductors of a different kind. During electrolysis, the cathode should serve as a carrier (receiving electrons from the cation), and the anode as an oxidizer (receiving electrons from anions). The essence of electrolysis is determined by the influence of the electrical energy of chemical reactions - the inspiration on the cathode (K) and the oxidation on the anode (A). These processes are called processes (reactions) of electro-energy and electro-oxidation. It is worth noting that the oxidizing effect of the electric struma has a rich variety of strengths for the development of chemical oxidizing agents and vibrators. Investigation of electroplating and rozchinіv elektrolіtіv.

Salt electrolysis

1) All metal cations are used on cathodes:

K(-): Zn2+ + 2e- → Zn0; Na+ + 1e- → Na0

2) Aniones of acid-free acids are oxidized on the anode:

A(+): 2Cl¯ - 2e-→Cl2

3) Anionic acids of cisnic acids dissolve hydrophobic acid oxide and acid:

A(+): 2SO42ˉ - 4e- → 2SO3 + O2

Electrolysis of water grades of electrolytes

The nature of the retailer, the material of the electrodes, the strength of the struma on them and other factors give a great boost to the process of electrolysis and the nature of the end products. In aqueous solutions of electrolytes, hydrated cations and anions, water molecules are present, which can also be subject to electrochemical oxidation. As the same electrochemical processes run on electrodes during electrolysis, deposit due to the value of the electrochemical potentials of the electrochemical systems.

Anode processes.

During the electrolysis of speech, vicor is inert, which does not change in the process of electrolysis of anodes (graphite, platinum) and retail anodes, which are oxidized in the process of electrolysis more easily, lower anions (from zinc, nickel, silver, midi and other metals).

1) Anions of non-acidic acids (S2?, I?, Br?, Cl?) at their sufficient concentration are easily oxidized to similar simple speeches.

2) During the electrochemical treatment of aqueous solutions of meadows, acidic acids and their salts, as well as hydrofluoric acid and fluoride, electrochemical oxidation of water is observed:

puddle roses: 4OH¯ - 4e- → O2 + 2H2O

in acidic and neutral varieties: 2H2O - 4e- → O2 + 4H+

Zastosuvannya elektrolizu. The removal of wholesome products in the way of electrolysis allows simply (regulating the strength of the struma) curing the consistency and directing the process, which is why it is possible to adjust the process like that of the "soft" ones, so in the borderline "zhorst" minds, oxidation or oxidation is stronger, otrimuyuchi. H2 and O2 from water, C12 from aqueous solutions of NaCl, F2 from melting KF into KH2F3 are produced by electrolysis.

Hydroelectric metallurgy is an important part of the metallurgy of color metals (Сu, Bi, Sb, Sn, Pb, Ni, Co, Cd, Zn); it will be zastosovuєtsya also for the selection of noble and rozsіyanih metals, Mn, Cr. Electrolysis vikoristovuyut without intermediary for the cathodic vision of metal after that, as a result of transfers from rudi to rozchin, and rozchin need to be cleaned. Such a process electroextraction. Electrolysis zastosovuyt also for cleaning metal - electrolytic. refining (electrorefining). This process is carried out in the anode separation of fermented metal and in the distant cathode sedimentation. Refining and electroextraction is carried out with rare electrodes from mercury and amalgams (amalgam metallurgy) and electrodes from solid metals.

Electrolysis of rozmeltiv elektrolitiv - an important way of virobnitstva many others. metals. So, for example, aluminum-lilac is removed by electrolysis of cryolite-alumina melt (Na3AlF6 + A12O3), purification of sulfur is removed by electrolysis. refining. In this case, the A1 melt should serve as an anode, which can contain up to 35% Cu (for tightness) and that which is found on the bottom of the electric bath. The middle ball of the bathtub should contain ВаС12, A1F3 and NaF, and the upper one - melting the refiner. A1 i є cathode.

Electrolysis melt magnesium chloride and aquatic carnalite - max. the most extensive way of extracting Mg. At prom. scales of electrolytic melting of vicorist for possession of puddles and alkaline-earth. metals, Be, Ti, W, Mo, Zr, U and in.

To electrolitich. ways of removing metals are also introduced to metal ions, other, more electro-restriction. metal. The use of metals in water enhancements also often includes the stage of electrolysis - electrochem. ionization of water and sedimentation of ions in metal for a wave of electrons, which vibrates with it. An important role is played by the processes of sleepy vision or the opening of December. metal, sawn metal vision there movlyav. water on the cathode and adsorption of components on the electrodes. Electrolysis vikoristovuyut for the preparation of metal. powders from the tasks of St. you.

BATTERIES electric (type lat. accumulator-selector, accumulator), chem. dzherela struma bagatorase diy. When charging, call out. Gerela electric. strum in the battery accumulates energy, like when discharging in the aftermath of chemicals. r-tsії without intermediary reshuffle. I'm new to the electrician and I see myself at the old house. lanceug. Behind the principle of robotics and basic. the elements of the construction, the batteries are not affected by the galvanic elements, but the electric r-tsії, and also the total strum-forming r-cіya in the accumulators werewolves. Therefore, after the discharge of the battery, you can re-charge the stream passing through the gate directly: on the arm. Electrode is utvoryuєtsya at tsimu okislyuvach, on the negative-researcher.

max. wide lead-acid batteries, often sv. also acidic. Їhnya diya is based on r-tsії:

Corrosion is a process of mimicry ruining of metal after fiz-chem. vzaєmodії іz navkolishnіm sredovischem. Behind the mechanism: chemical and electrochemical.

Chemical destruction of metal during iodine oxidation without vinification of the electric jet. Electrochemical destruction of the metal in the middle of the electric strum for the middle of the electric jet system.

Corrosion on parts and nodes of engines, gas turbines, rocket launchers. Chemical corrosion occurs in the process of metal processing at high temperatures and pressure.

Electrochemical corrosion can occur: in electrolytes, soil, in the atmosphere of any water gas.

As a defense against corrosion, it is possible to zastosovuvatysya applied any kind of coating, as if changing the adoption of a corrosive element (passive method)

Barviste cover, polymer cover and enamel are guilty, first for everything, forbid access to sourness and vology. Often, the coating is also stagnant, for example, other metals have become, such as zinc, tin, chromium, nickel. Zinc coating protects the steel if it is often coated. Zinc has a negative potential and corrodes first. They are Zn2+ toxic. When preparing cans, put a plaque on it, covered with a ball of tin. On the surface of galvanized zherst, when the ball is rubbed, the tin is corroded, moreover, it is hardened, it starts to be cold, so that the tin has a greater positive potential. Another possibility to protect metal against corrosion is to put a protective electrode with a great negative potential, for example, zinc or magnesium. For whom the corrosive element is specially created. The metal that is being protected acts as a cathode, and this kind of shield is called a cathode shield. The rozchinny electrode is called as an anode of tread protection. This method is used for protection against corrosion of sea vessels, bridges, boiler installations, pipes laid under the ground. To protect the ship's hull, zinc plates are attached to the outer side of the hull.

In addition to equalizing the potential of zinc and magnesium from the cold, stench may have greater negative potential. Prote to corrode the stench more later on the surface of the oxide smelting, as it protects the metal from further corrosion. The adoption of such a bath is called the passivation of metal. In aluminum її posilyuyut anodic oxidation (anoduvannya). When a small amount of chromium is added to steel, oxide melting is established on the surface of the metal. Instead of chromium in stainless steel - over 12 vіdsotkіv.

Cathodic protection against corrosion

Cathodic electrochemical protection in the form of corrosion zastosovuetsya then, if the metal, which is protected, is not weak to passivation. This is one of the main types of metal protection against corrosion. The essence of the cathode shielding is polarizing at the addition to the level of the oval strum at the negative pole, which polarizes the cathodes of the corrosive elements, approaching the potential value to the anode ones. The positive pole of the struma is attached to the anode. With any corrosion of the structure, which is protected, it may be reduced to zero. The anode gradually collapses and it is necessary to periodically change it.

Іsnuє kіlka options for cathode protection: - polarization from the outside of the dzherel of the electric stream; change in the speed of the cathode process (for example, deaeration of electricity); contact with metal, which has the potential for strong corrosion in this medium is more electronegative (the so-called protective shield).

The polarization in the form of a splendid dzherel of an electric strum is more often for the protection of spores, which are found near the ground, water (the bottom of the ships is thin). In addition, this type of corrosion protection is applied to zinc, tin, aluminum and other alloys, titanium, copper and other alloys, lead, as well as high-chromium, carbonaceous, alloyed (as low and high-alloyed) steels.

Serve as a strum dzherel to serve as a cathode shielding station, as it consists of a vipryamlyach (transformer), a strum feeder to the point that is protected, an anode grounding electrode, an anode electrode and an anode cable.

Cathodnius Zachist zastosovuetsya like an independent, and additive kind of corrosive zahistu.

The main criterion, which can be used to judge the efficiency of cathodic protection, is the protection potential. Let's name the potential, with some kind of corrosion metal in the singing minds of the navkolishny middle ground, it gains the lowest (as little as possible) meaning.

Vikoristan cathodic zahistu has nedolіki. One of them is the danger of perezahist. The perezakhist is afraid of the great potential of the object, which is being protected, in a negative beak. Whom is seen. As a result - ruinuvannya sour coatings, water-sprayed metal, corrosive cracking.

Protector Zakhist(Tread wear)

A variety of cathodic protection is protective. When vikoristanny tread protection to the object that is being protected, metal comes with a greater electronegative potential. With this, it is not the structure that collapses, but the protector. Over the years, the protector corrodes and it is necessary to replace it with a new one.

Protective protection is effective in depressions, if there is a small transitional opir between the protector and the middle middle.

The leather protector has a maximum radius of protection, which is the maximum possible distance, on which it is possible to see the protector without wasting a protection effect. Zastosovuetsya tread protection most often, if it is impossible, it is important that it is expensive to lead to the design of the strum.

Protectors vikoristovuyutsya for zakhistu sporuds in neutral mediums (sea and river water, again, soil and in.).

For the preparation of vicorist protectors, such metals are used: magnesium, zinc, iron, aluminium. Pure metals do not vanquish the whole world of their functions, so when the protectors are prepared, they will easily fit.

Zalіznі protectors are made from carbon steels or pure galіza.

Corrosion Inhibitors, chemical compositions or compositions, the presence of which in small quantities in an aggressive medium increases the corrosion of metals. Zahisna diya іngіbіtorіv korozії zaumovlenа zmіnou stanu surfіnі metal vnaslіdok adsorptії (adsorptії іngіbіtori korozії) аbо dіya іnami іnіbіtorіv korozії аbоut dіya іnіmі іnіmі mаl іn important spoluk. Residue on the surface of the slab, as if it were thinner for the conversion protection of the coating (div. Protection against corrosion). Upovіlnennya koroz_ї vіdbuvaєtsya through zmenshennya ploshchі active surfy metal and zmіni energії aktivії elektrodnih reaktsіy, scho limit foldable korozіyny process. Corrosion inhibitors can galvanize the anode separation and increase the pasivation of metal (anodic corrosion inhibitors), reduce the cathode process speed (cathode corrosion inhibitors) or improve the damage to the processes (corrosion corrosion inhibitors).

The values of oxidative-oxidative potentials can be used to judge the direct flow of oxidative-oxidative reactions. Vihodjachi z vnyannia (7.4), as po'yazu variance of potential napіvreaktsiy zmіnoy volnoї energії Gibbs DG, and remembering that the possibility of passing through any chemical process is implied:

Oxide-water reaction will miraculously proceed in such a straight line, with a greater increase in the oxide-water potential, it will act as an oxidizer in terms of temperature to the heat reaction with a lower potential.

It is safe for him that in the tables the value of j 0 is indicated for the reaction to one directly - oxidation.

In other words, an oxidative-reactive reaction can occur in that case, as long as the difference in the potentials of the reaction of the galvanic cell is positive.

In the world, the reaction of the concentration of the oxidized and the derived forms in the reactions change in such a way that the potential of the oxidizer changes, and the potential of the agent grows. As a result, the difference in potentials changes, the disruptive power of the process is weaker. The oxide-water reaction will continue until the potential of the reaction does not become equal. For the equanimity of potentials, the system is equipped with chemical equanimity.

In the first place, close to the same way, the standard potentials of the reaction can be changed nutritionally - as they are built, the function of the oxidizing agent is completely different. For which standard potentials can be substantiated one kind of one. For example, zinc (j 0 \u003d -0.76) will add (remove) copper (j 0 \u003d +0.34) from the water level of salt, with any practical concentration of this difference. But, since the difference in standard potentials is small (standard potentials are close), it is necessary to develop effective potentials with equal concentrations (7.2)
new reactions.

butt 12 Set the possibility that the reaction proceeds directly

2KBr + PbO 2 + 2H 2 SO 4 = Br 2 + PbSO 4 + K 2 SO 4 + 2H 2 O.

Solution. In order to test the power, we write the reaction in ionic form, dividing it into the reactions, and write the standard potentials of the reactions:

2Br - + PbO 2 + 4H + = Pb 2+ + Br 2 + 2H 2 O.

1) Br 2+2? = 2Br -; j 0 \u003d 1.09 B,

2) PbO2+4H++2? = Pb 2+ + 2H 2 O; j 0 \u003d 1.46 V.

Behind the virase (7.4) Dj \u003d j ok-la - j east-la \u003d 1.46 - 1.09 \u003d 0.37> 0.

Father, DG< 0, т.е. реакция будет протекать слева направо. Из сопоставления потенциалов видно, что PbO 2 в кислой среде имеет больший потенциал, следовательно, он может окислить ионы Br - , которые образуют при этом Br 2 .

butt 13 Determine the possibility of overshooting oxide-water reactions

a) HBrO + HIO \u003d HBrO 3 + HI,

b) HBrO + HIO = HBr + HIO3.

Solution. Let's write down the different types of reactions and the different potentials: for the reaction a)

BrO 3 - + 5H + +4? = HBrO + 2H 2 O; j 0 \u003d 1.45 B,

HIO + H + +2e \u003d I - + H 2 O; j 0 \u003d 0.99 B.

Vicorist equal (7.3), we know the difference in oxide-water potentials

Dj 0 \u003d j 0 ok - j 0 restore \u003d 0.99 - 1.45 \u003d -0.46 V.

Oskilki Dj 0< 0, то DG >0, then, the reaction is impossible (it will flow directly).

For reaction b)

НBrO + H++ 2? = Br - + H 2 O; j 0 \u003d 1.33 B,

IO 3 - +5H++4? = HIO + 2H 2 O; j0 = 1.14.

Dj 0 \u003d j 0 ok - j 0 restore \u003d 1.33 - 1.14 \u003d 0.19 B. Scales for the reaction Dj 0\u003e 0, then the reaction is possible.

Example 14. Can Cr 3+ ions be oxidized to Cr 2 O 7 2 - diyu NO 3 - -one?

Solution. As an oxidizing agent, the NO 3 ion - converts to NO, which is why the potential for offensive reactions:

NO 3 - + 4H + +3? = NO + 2H 2 O; j 0 \u003d 0.96 B,

Cr 2 O 7 2 - + 4H + + 6? = 2Cr 3+ + 7H 2 O; j 0 \u003d 1.33 V.

Dj 0 \u003d j 0 ok - j 0 restore \u003d 0.96 - 1.33 \u003d -0.37 U. DG\u003e 0, then. NO 3 - -ion cannot be oxidized by conversion to Cr 3+ -ion in standard minds.

Navpak, doromic acid H 2 Cr 2 O 7 and її salts ("bichromate") oxidize NO HNO 3.

Oxide - dnovlyuvalny potential є okrem, narrow fluctuation of the understanding of the electrode potential. Let's look at the report and understand it.

AT OVR electronic transmission guides to oxidizers is produced by direct contact of the particles, and the energy of the chemical reaction is transformed into heat. Energy be-yaka OVR, which flows in different ways, can be converted to electricity. For example, as an oxidizing-redundant process, expand the space, tobto. the transfer of electronics by the conductor must be carried out through the conductor of electricity. It is implemented in galvanic cells, where electrical energy comes out of chemical energy.

Let’s take a look, in the lion’s vessel, we have filled the zinc sulfate ZnSO 4 with a zinc plate lowered into the new zinc plate, and to the right vessel, we have lowered the mid-range sulfate CuSO 4 into the new mid plate.

Interaction between the difference and the plate, as if acting like an electrode, so that the electrode added an electric charge. The difference in potentials, which is the cause of the difference between the metal-rozchins of electricity, is called electrode potential. Its meaning and sign (+ or -) are assigned by nature to the difference and metal, which is known in the new. When metals are saturated, the active salts (Zn, Fe and others) are negatively charged, and the less active ones (Cu, Ag, Au and others) are positively charged.

As a result of the insertion of a zinc and a copper plate by an electric conductor, the electric conductor is charged into the lansyug of an electric stream for a rahunka.

At this point, there is a change in the number of electrons in zinc, which is compensated by the transition of Zn 2+ to change. sizing of the zinc electrode - anode (oxidation process).

Zn - 2e - = Zn 2+

At its core, the increase in the number of electrons in the midi is compensated by the discharge of the ions in the midi, which can be dispersed, which leads to the accumulation of midi on the mid electrode. cathodes (renewal process):

Cu 2+ + 2e - = Cu

In this order, in the element, there is such a reaction:

Zn + Cu 2+ = Zn 2+ + Cu

Zn + CuSO 4 \u003d ZnSO 4 + Cu

Kіlkіsno characterize oxidation-recovery The processes allow for electrode potentials similar to a normal water electrode (the potential is taken equal to zero).

Shchob to signify standard electrode potentials vikoristovuyut element, one of the electrodes of which is the testing metal (or non-metal), and the other is the water electrode. For the known difference of potentials at the poles of the element, the normal potential of the reached metal is determined.

Oxide-water potential

The values of the oxidation-water potential are corrosive in different situations, depending on the direct overshoot of the reaction in water and in other areas.

Let's carry out the reaction

2Fe 3+ + 2I - = 2Fe 2+ + I 2

in such a way that iodide-ioni and ioni exchanged their electrons through the explorer. At the judge, scho to revenge the differences Fe 3+ і I - perhaps inert (platinum and yellow) electrode and closed inner and outer lance. Lancey has an electric strum. Iodide-ioni give out their electrons, so they pass through the conductor to an inert electrode, immersed in Fe 3+ salt:

2I - - 2e - = I 2

2Fe 3+ + 2e - = 2Fe 2+

Oxidation-renovation processes are carried out on the surface of inert electrodes. The potential, which is blamed on the inter-inert electrode - razzin and vengeance as oxidized, so i recreated the form of speech, is called equally important oxide-leading potential. The value of the oxide-water potential to deposit in the bagats factors, zocrema such:

The nature of speech(oxidizing that vodnovnika)
Concentration of oxidized and derived forms. At a temperature of 25 ° C vice 1 atm. the value of the oxidizing potential should be paid for additional help river Nernst:

E=E° + (RT/nF) ln (C ok / C sun), de

E - oxide-water potential of the wager;

E°- standard potential C ok =C all);

R - gas steel (R = 8.314 J);

T - absolute temperature, K

n is the number of electrons that are either used or maintained in the oxide-water process;

F - became Faraday (F = 96484.56 C / mol);

C ok - Concentration (activity) of the oxidized form;

C all - concentration (activity) of the inspired form.

Substituting in equalizing given data and moving up to the tenth logarithm, we take away the offensive form of equalizing:

E=E° + (0,059/ n) lg (C ok /C sun)

At C ok >C all, E>E° and navpaki, yakscho C ok< C all, then E< E°

Acidity varies. For couples, the oxidized form is oxidized to prevent acid (for example, Cr 2 O 7 2-, CrO 4 2-, MnO 4 -) with a change in pH, the oxidation-oxidation potential increases, tobto. growth potential over the growth of H+. First of all, the oxidizing potential decreases with changes in H+.
Temperature. With an increase in temperature, the oxide-water potential of the vapor also increases.

Standard oxidizing-conditioning potentials are presented in the tables of special indicators. The mother's trace on the uvaz, which only reactions are seen in water roses at a temperature of 25°C. Such tables can give you the ability to work out deeds of visnovka:

The value and the sign of the standard oxidizing and oxidizing potentials, allow the transfer of power (oxidizing or redundant) to reveal atoms, ions or molecules in chemical reactions, for example

E°(F 2 / 2F -) \u003d +2.87 V - the strongest oxidizer

E°(K + / K) \u003d - 2.924 V - the strongest driver

Given a pair of matim, more powerful building, more numerically significant negative potential, and more oxidizing building, more positive potential.

It is possible to designate as the basis of one element to be the mother of the most powerful oxidizing or inspiring authority.
It is possible to transfer directly OVR. It seems that the robot of a galvanic cell can have a mind, that the difference in potentials can be positively significant. Overshooting the OVR with a chosen one directly is also possible, as the difference in potentials may be positively significant. OVR occurs in weak oxidizers and in the strong ones, for example, reaction

Sn 2+ + 2Fe 3+ = Sn 4+ + 2Fe 2+

Mayzhe leaks directly, because

E°(Sn 4+ /Sn 2+) = +0.15, and E°(Fe 3+ / Fe 2+) = +0.77, tobto. E°(Sn4+ /Sn2+)< E°(Fe 3+ / Fe 2+).

Cu + Fe 2+ = Cu 2+ + Fe

Impossible in a straight line and flowing only on the right

E°(Сu 2+ /Cu) = +0.34, and E°(Fe 2+ / Fe) \u003d - 0.44, tobto. E°(Fe 2+ /Fe)< E°(Cu 2 + / Cu).

In the process of OVR, the number of cobs of speeches changes, due to which E oxidizing decreases, and E grows. At the end of the reaction, tobto. at the same time, the current chemical level has the potential to reverse both processes.

Yakshcho for tsikh minds, it is possible to break dekіlkoh OVR, then we are in front of that reaction, which has the greatest difference in oxidizing and oxidizing potentials.
Koristuyuchis dovodkovymi denim, you can determine the EPC reaction.

Otzhe, How to designate an EPC reaction?

Let's take a look at a few reactions and significant EPCs:

Mg + Fe 2+ \u003d Mg 2+ + Fe
Mg + 2H + = Mg 2+ + H 2
Mg + Cu 2+ \u003d Mg 2+ + Cu

E°(Mg 2+ / Mg) \u003d - 2.36 V

E°(2H + /H 2) = 0.00 V

E°(Cu 2+ / Cu) = +0.34 V

E°(Fe 2+ / Fe) \u003d - 0.44 V

To determine the EPC reaction, it is necessary to know the difference in the potential of the oxidizing agent and the potential of the agent

EPC \u003d E 0 ok - E 0 out

EPC \u003d - 0.44 - (- 2.36) \u003d 1.92 V
EPC = 0.00 - (- 2.36) = 2.36 V
EPC \u003d + 0.34 - (- 2.36) \u003d 2.70 V

Mustache guessing reactions can run straight, because їх ЕРС > 0.

Equity constant.

If you blame the need for a specific step to overshoot the reaction, then you can speed up the constant of jealousy.

For example, for the reaction

Zn + Cu 2+ = Zn 2+ + Cu

Zastosovuyuchi chinnyh mas law, you can write

K = C Zn 2+ /C Cu 2+

Here equalization constant shows equally important spivvіdnoshennia concentrations of ions in zinc and midi.

The value of the equalization constant can be changed by freezing river Nernst

E=E° + (0,059/ n) lg (C ok /C sun)

Let us represent the value of the standard potentials of Zn/Zn 2+ and Cu/Cu 2+ pairs, we know

E0 Zn/Zn2+ = -0.76 + (0.59/2)logC Zn/Zn2 ta E0 Cu/Cu2+ = +0.34 + (0.59/2)lgC Cu/Cu2+

Become jealous E0 Zn/Zn2+ = E0 Cu/Cu2+, tobto.

0.76 + (0.59/2) logC Zn 2 = +0.34 + (0.59/2) logC Cu 2+, stars are acceptable

(0.59/2) (lgC Zn 2 - lgC Cu 2+) = 0.34 - (-0.76)

logK = log (C Zn2+ /C Cu2+) = 2(0.34 - (-0.76)) / 0.059 = 37.7

The value of the equal constant shows that the reaction may be residual, that is. doti, while the concentration of ions in mid-stane is 10 37.7 times less, the concentration of ions in zinc is lower.

Equity constantі oxide-water potential tied with a spelled formula:

lgK \u003d (E 1 0 -E 2 0) n / 0.059, de

K - equalization constant

E 1 0 and E 2 0

n is the number of electrons, which are considered to be redundant or oxidizing.

Yakscho E 1 0 > E 2 0 then lgK > 0 and K > 1. Also, the reaction proceeds in a straight line (angry to the right) and even though the difference (E 1 0 - E 2 0) is large, there is still enough left.

Navpaki, yakscho E 1 0< E 2 0 , то K будет очень мала . The reaction proceeds directly, because equal strongly shifted to the left. Since the difference (E 1 0 - E 2 0) is insignificant, then і K ≈ 1 and the reaction is not going to the end, so you can’t create the necessary minds for others.

Knowing the value of the equalization constant Without going into details, one can judge the depth of the chemical reaction. Keep in mind that given the value of the standard potentials, it is impossible to indicate the stability of the established equal reaction.

Based on the table of oxidation-oxidation potentials, it is possible to calculate the values of the equalization constants for approximately 85,000 reactions.

How to fold the circuit of a galvanic cell?

EPC element- The value is positive, because at the galvanic element of the robot to seep through.
EPC value of galvanized lance- the sum of the streak potentials at the boundaries of the separation of all phases, but, if there is oxidation on the anode, then the value of the cathode potential is taken into account the value of the anode potential.

In this order, when folding the circuit of a galvanic cell levoruch write down the electrode on which it is used oxidation process (anode), a on right- electrode, on which it is used renewal process (cathode).

Phase Cordon signified by one boundary - |
Electrolytic place on the border of two conductors are indicated by two characteristics - ||
Rozchini, in yakі zanureniya elektrolitny mіstok written in levoruch and right-handed in a different way (as it is necessary, the concentration of differences is immediately indicated). Components of one phase, with which they are recorded through a coma.

For example, warehouse galvanic cell diagram, In which the reaction occurs:

Fe 0 + Cd 2+ = Fe 2+ + Cd 0

For a galvanic cell, the anode is a flood electrode, and the cathode is cadmium.

Anode Fe 0 | Fe2+ | | CD 2+ | CD 0 Cathode

You will know typical tasks with solutions.