formulas
l loss of oxygen, but also drop too, negative electronic deactivation.
principles
writing electrode reaction of formula
The reaction principle of the electrode is substantially oxidation-reduction reaction, to follow the conservation of mass, conservation and electron charge conservation. In addition to also follow:
1. Additivity principles: Scheme adding two electrodes, erasing the electronic battery was overall reaction. With this principle, the overall cell reaction formula subtracting a known electrode reaction formula to give another electrode reaction equation.
2. Coexistence Principle: alkaline solution, CO 2 not exist, there will not be generated H + or reacted; Similarly the acidic solution, there will be reacted OH or carbonate ions will not be generated The presence. According to this principle, the electron gains and losses material be different in different media environments present in form. We can be written according to the pH of the electrolyte solution, to determine H 2 O, OH - , H + left or right in the equation.
1. Write the electrode reaction as well as the battery device 2. The writing Books electrode reaction of the battery based on the total reaction 3. Writing Writing secondary battery electrode reaction of the fuel cell 4. The electrode reaction and the like.
skill
1. Two electrodes accurately determine
Example 1. Zinc sheet and the aluminum sheet is connected with a wire, are inserted into dilute sulfuric acid, concentrated sulfuric acid, to write two primary battery and a battery-type electrode reaction Scheme. Analysis: When the sulfuric acid as an electrolyte solution, is more active aluminum oxide, the evolution of hydrogen on the zinc sheet, so that: the negative electrode (aluminum sheet): 2Al - 6e - == 2Al 3 + The positive electrode (zinc sheet): 6H + + 6e - == 3H 2 ↑ cell reaction: 2Al + 6H + < / sup> == 2Al 3 + + 3H 2 ↑ concentrated sulfuric acid as an electrolyte solution, at room temperature due to the passivation of aluminum occurs a phenomenon in concentrated sulfuric acid, and zinc can and The reaction concentrated sulfuric acid, so in this case as the anode zinc sheet, aluminum sheet as a positive electrode: negative electrode (zinc flakes): Zn - 2e - == Zn 2 + of the positive electrode (aluminum sheet ): 4H + + SO4 2 - + 2e - == SO 2 ↑ + 2H 2 O cell reaction: Zn + 2H 2 SO 4 (conc.) == ZnSO 4 + SO 2 ↑ + 2H 2 O
2. Note that the use of total cell reaction of formula
Example 2. The platinum wire is inserted into a KOH solution as an electrode, and then methane and oxygen are fed to the two electrodes, a galvanic cell. The methane into a very ______ battery electrode, the electrode reaction is extremely __________. Analysis: oxidation of methane combustion reduction reaction occurs: CH 4 + 2O 2 == CO 2 + 2H 2 O, alkaline solution, CO 2 can not release out: CO 2 + 2OH - == CO 3 2 - + H 2 O, so that the overall cell reaction is: CH 4 + 2O 2 + 2OH - == CO 3 2 - + 3H 2 O. Through the oxidation of methane occurs a pole, it is negative. The positive electrode absorbs oxygen, the oxygen may be regarded as the occurrence of corrosion: 2O 2 + 4H 2 O + 8e - == 8OH - < / sup>, a positive reaction obtained by subtracting the total reaction negative reaction: CH 4 + 10OH - - 8e - == CO 3 2 - + 7H 2 O
3. Follow the electrolyte solution is pH
Example 3. Hydrogen fuel cell using the U.S. Apollo spacecraft is a new chemical power. ⑴ with KOH as an electrolyte solution, the water generated by electrode reaction, and then the condensed potable water can be used as astronauts, the reaction is: 2H 2 + O 2 = = 2H 2 O, respectively, the electrode reaction of formula ___________; ⑵ such as KOH to the dilute H 2 SO 4 as the conductive material, of the electrode reaction is ___________. Analysis: for battery applications, the electrolyte participate in the electrode reaction, but in the course of the reaction only serve as a bridge, such as acid electrolyte, H + to participate in an electrode reaction, but the reaction must be the other electrode H < sup> +generation, while not appear OH - ; alkaline electrolyte has a similar situation. Answer: ⑴ anode: 2H 2 + 4OH - - 4e - == 4H 2 O, cathode: O 2 + 2H 2 O + 4e - == 4OH - ; ⑵ anode: 2H 2 < / sub> - 4e - == 4H + , a positive electrode: O 2 + 4H + + 4e - == 2H 2 O.
4. Full use of the principle of conservation of charge in the same primary battery, the negative electrode will be the number of electrons lost equals the number of electrons obtained positive electrode, the electrode reaction at the time of writing the formula, to pay attention to charge conservation. This will avoid overwriting the overall reaction formula to errors caused by the electrode reaction, but also to avoid errors in the relevant calculation.