How do chemistry masters memorize these electrode equations, ask for advice, and be satisfied with t

First of all, you have to understand the essence, hydrogen and oxygen fuel cells are batteries with hydrogen and oxygen as raw materials, so regardless of neutral, acid, alkali, the reactants of its electrode reaction and chemical reaction are H2 and O2.

Then the reaction is H2, O2 reaction to produce water, and you can note the neutral electrode reaction. H2 can only lose electrons and become hydrogen ions, and O2 can only gain electrons and become hydroxide.

Acidic means that there are a large number of hydrogen ions, then H+ will react with hydroxide, so the positive reaction will change.

Alkaline means that there is a large amount of hydroxide, then oh- will react with hydrogen ions, so the negative electrode reaction will change.

The key is to understand, you don't need to remember if you understand, say a method, you first remember the reaction formula of the neutral medium, and then think, there are hydrogen ions in the acidic medium, then it will be combined with the hydroxide produced by the positive reaction in the neutral medium to form water, that is, the positive electrode equation is added on both sides of the equation at the same time to obtain the positive electrode reaction in the acidic medium. However, there is hydroxide in the alkaline medium, which will combine with the hydrogen ions generated by the negative electrode in the neutral medium to form water, that is, four hydroxide radicals are added on both sides at the same time to obtain the negative electrode reaction formula. The rest is the same.

We assume that the neutral is 0, then according to the pH, the acidity is negative, the alkalinity is positive, so the acidic medium, what medium produces what ions, the acidity produces h ions, because the acidity is negative, so we are the negative electrode to produce hydrogen ions, the positive electrode reaction is 2h2 + 02 = 2h20 of the medium reaction minus the negative electrode reaction equation, similar to alkalinity, and neutral is the acidic negative electrode plus the basic positive electrode.

First remember the material before the reaction of the positive and negative electrodes, then think about whether they should gain electrons or lose electrons, then know the product, then look at the medium, and then trim.

You memorize a simple one, and then subtract the electrode reaction you memorized from its total reaction to get another electrode reaction.

There is no OH- in acidic conditions and H+ in alkaline conditions

Friends, you can watch it directly.

The method of writing the electrode reaction equation is as follows: according to the electrochemical principle, the negative electrode of the galvanic cell undergoes an oxidation reaction, the positive electrode undergoes a reduction reaction, the electrolytic cell anode undergoes an oxidation reaction, and the cathode undergoes a reduction reaction.

Writing of electrode reactive formulas in galvanic cells:

1. First determine the positive and negative electrodes of the galvanic battery, list the reactive substances on the positive and negative electrodes, and mark the gains and losses of the same number of electrons.

2. Pay attention to whether the cation generated by the negative electrode reaction and the anion in the electrolyte solution coexist. If it does not coexist, the anions in the electrolyte solution should be written into the negative reaction formula; If the reactive species on the cathode is O2 and the electrolyte solution is neutral or basic, then water must be written into the positive reaction formula and O2 generates OH-, if the electrolyte solution is acidic, then H+ must be written into the positive reaction formula and O2 generates water.

3. The positive and negative electrode reaction formulas are added to obtain the total reaction formula of the battery reaction. If the total reaction formula of the battery reaction is known, the electrode reaction formula that is easier to write can be written first, and then on the basis of the conservation of electrons, the total reaction formula can be subtracted from the electrode reaction formula that is easier to write, that is, the electrode reaction formula that is more difficult to write can be obtained.

Writing of the electrode reaction formula in the electrolytic cell:

1. First of all, look at the anode material, if the anode is a reactive electrode (before the metal activity sequence table AG), it should be the anode that loses electrons, the anode is constantly dissolved, and the anions in the solution cannot lose electrons.

2. If the anode is an inert electrode (PT, AU, graphite), it should be an ion discharge in the electrolyte solution, and the electrode reaction formula should be written according to the discharge sequence of the ions. The anode (inert electrode) undergoes an oxidation reaction, and the anion loses electrons and is oxidized in the following order: S2- SO32- I-br-Cl-OH- OH-oxylate ion of water ionization F-.

3. The cathode undergoes a reduction reaction, and the order in which the cations get electrons is reduced is: AG+ Hg2+ Fe3+ Cu2+ (H+ ionized by acid) Pb2+ SN2+ Fe2+ Zn2+ (H+ ionized by water) Al3+ Mg2+ Na+ Ca2+ K+. (Note:.)

In the aqueous solution, Al3+, Mg2+, Na+, Ca2+, K+ are not reduced, and the smelting of these active metals is often prepared by electrolysis of anhydrous molten salts or oxides).

4. Since the electrode material is graphite, which is an inert electrode and does not participate in the electrode reaction, the writing of the electrode reaction formula only considers the ion discharge sequence in the solution. The ionized field cha that moves to the anode has Cl- and the oh- ionized by water, but the discharge on the anode is Cl-; The cations moving towards the cathode are Na+ and H+ separated from the hydroelectric sonata, but the ones that are discharged at the cathode are H+.

Electrode equation: The formula that represents the electrode reaction that occurs in a galvanic cell or electrolytic cell

The electrode reaction formula refers to the formula source bench in the electrochemical device that indicates the oxidation or reduction reaction of atoms or ions on the electrode.

Principle: Electrode reactions are basically redox reactions, which should follow the conservation of mass, electron and charge. In addition to this, follow the following:

1. Additivity principle: the two electrode reaction formulas are added, and the total reaction formula of the battery is obtained after the electrons are removed. Using this principle, the total reaction formula of the battery is subtracted from the known reaction formula of one electrode to obtain the reaction equation of the other electrode.

2. Principle of coexistence: CO2 cannot exist in alkaline solution, and there will be no H+ to participate in the reaction or generation; Similarly, in acidic solutions, there will be no OH to participate in the reaction or be generated, and there will be no presence of carbonate ions.

According to this principle, the form in which a substance gains and loses electrons in different media environments is different. We can write according to the acidity and alkalinity of the electrolyte solution to determine whether H2O, OH-, H+ is on the left or right side of the equation.

At the same time, there is 1Write the electrode reaction according to the battery device diagram 2Write the electrode reaction according to the total cell response3Writing of the electrode reaction of the secondary battery 4Writing of fuel cell electrode reactions, etc.

Make full use of the principle of conservation of charge In the same galvanic cell, the number of electrons lost by the negative electrode must be equal to the number of electrons obtained by the positive electrode, so when writing the electrode reaction formula, it is necessary to pay attention to the conservation of charge. In this way, the mistakes caused by the rewriting of the total reaction formula to the electrode reaction formula can be avoided, and errors in the calculation can also be avoided.

In the galvanic cell reaction, the active one pole is the negative electrode, and the one with poor activity is the positive electrode.

Or with combustibles as the negative electrode and oxygen as the positive electrode (fuel cell).

In general, the concept of electrons should not be introduced in the analysis.

The positive electrode emits current, and the valency decreases (in general, cations in solutes are precipitated by price reduction, such as Cu + to Cu H + to H2, and cations are difficult to precipitate, such as K, Ca, Na, then O2 is changed by water to OH- Fuel cells, and generally O2 is changed by water to OH-).

Reaction formula: Xn+ +Ne-=X or O2+2H2O+4E-=4Oh-

The negative electrode accepts the current and the valency increases (generally the valency of the electrode increases, dissolving, such as Zn becomes Zn+ fuel cell, C binds OH to CO2 and adds water, H binds OH- to water).

Reaction formula: X-Ne-=Xn+ or CMHN+OH-=MCO2+(N+2M)H2O

In this case, electrons can be introduced, and the outflow current is the receiving electron (+e-), and the receiving current is the release of the electron (-e-).

The positive and negative electrode reactions are added to obtain the total reaction formula of the battery reaction. If the total reaction formula of the battery reaction is known, the writing electrode reaction formula that is easier to write can be written first, and then on the basis of the conservation of electrons, the total reaction formula is subtracted from the writing electrode reaction formula that is easier to write, that is, the writing electrode reaction formula that is more difficult to write can be obtained.

Examples. Insert a metal platinum sheet into the KOH solution as an electrode, and pass methane and oxygen respectively on the two poles to form a methane-oxygen fuel cell, the ion equation of the battery reaction is: CH4+2O2+2OH-=CO32-+3H2O, and try to write the two-pole reaction formula of the battery.

Analysis: From the perspective of the total reaction formula, the electrons obtained by O2 participate in the positive electrode reaction, and in the alkaline solution, the electrons obtained by O2 generate OH-, so the positive reaction formula is: 2O2+4H2O+8E-

8oh-。The reaction formula on the pole of negative intestinal plaque and the elimination of the cyclic pole can be obtained by subtracting the positive reaction formula (conservation of electrons) from the total reaction formula to obtain CH4+10OH- 8E-=

co32-+7h2o。

If you are given a diagram, first analyze the positive and negative electrodes, and then write the reaction formula according to the positive and negative reaction laws. If you are given the total reaction formula, it will be written according to whether it is oxidation or reduction.

As for writing the formula, it is the ion equation plus the gain or loss of electrons, and pay attention to the conservation of electrons.

If you gain electrons, you will increase, and if you lose, you will subtract; Electronic symbol: the electron is the secondary, and the loss is positive.

The total reaction formula is the sum of the two pole reactions.

First, as long as it is a chemical reaction, it must conform to the law of conservation of mass, and of course electrochemical reactions are no exception, that is, the reaction equation must be balanced. (This is the last step to do).

Second, electrochemical reactions generally occur in electrolyte solutions, so there must be ionization, hydrolysis and interionic reactions, etc., so they must conform to the law of conservation of charge, that is, the total number of charges before and after the reaction remains unchanged. (This will be encountered in writing the ionic equation for the electrochemical reaction and should be verified after trimming).

Thirdly, and most importantly, the electrochemical reaction must have electron gain and loss, and the valency of the element rises and falls, that is, it belongs to the redox reaction, so it must conform to the law of conservation of the total number of electrons gained and lost.

The specific way to write the equation for an electrochemical reaction should be:

First of all, it is determined that ** is the positive and negative electrodes of the galvanic cell or the cathode and anode of the electrolytic cell, which is mainly determined by the redox (metal activity) or the discharge order of ions (clusters) of the elements. In galvanic cells, whoever is active in the two (or more) metals acts as the negative electrode, that is, an oxidation reaction occurs and electrons are lost; The other least reactive metal acts as the cathode, while the cation of the electrolyte (note: not the metal) undergoes a reduction reaction to obtain electrons.

In the electrolytic cell, the two (or more) cations are discharged first, and the cathode is used as the cathode, and the reduction reaction occurs to obtain electrons; Two (or more) anions are discharged first and the anode is used as the anode, and oxidation reactions occur and electrons are lost. (Note: If it is an aqueous solution in the electrolytic cell, the hydrogen ions and hydroxide ions ionized by water should be considered).

pt2+>au3+>ag+>hg2+>fe3+>cu2+>h+>pb2+>sn2+>fe2+>zn2+>al3+>mg2+>na+>ca2+>k+>nh4^+>sr2+>rb+>ba2+>cs+

Anion: P3->S2->I->Br->Cl->OH->All oxylate ions》 F-

Second, write out the electrode half-reaction. Note: Charge is conserved. For example: Cu2+

2e==cu，4oh-

o2 (ascending sign) +

2H2O4E Finally, two halves were added and combined.

Or you can directly determine the oxidant and reducing agent of the whole reaction, and clarify the oxidation products and reduction products, and then balance according to the leveling method of the redox reaction.