Lead storage battery cells

In an electrochemical cell, electrical work is obtained from an oxidation-reduction reaction. For example, consider the process that occurs during the discharge of the lead storage battery (cell). Figure 9.3 shows a schematic drawing of this cell. One of the electrodes (anode)q is Pb metal and the other (cathode) is Pb02 coated on a conducting metal (Pb is usually used). The two electrodes are immersed in an aqueous sulfuric acid solution. 

Cross-sectional diagram of a lead storage battery cell. 

The rechargeable 12-V lead storage battery used in automobiles consists of six voltaic cells of the type shown in Figure 18.12. A group of lead plates, the grids of which are filled... 

In a folly charged lead storage battery, tire electrolyte consists of 38% sulfuric add by mass. The solution has a density of 1.286 g/cm3. Calculate E for tire cell Assume all the H+ ions come form tire first dissociation of H2SO4, which is complete. 

Fig. 22-10. Cells from Edison and lead storage batteries (schematic).

Figure 9.3 The lead storage battery. The key to obtaining electrical energy from a redox chemical reaction is to physically separate the two half-cell reactions so that electrons are transferred from the anode through an external circuit to the cathode. In the process, electrical work is accomplished.

To apply the features that characterize galvanic cells, Example describes the lead storage battery. 

The electrical current needed to start an automobile engine is provided by a lead storage battery. This battery contains aqueous sulfuric acid in contact with two electrodes. One electrode is metallic lead, and the other is solid Pb02. Each electrode becomes coated with solid PbSOq as the battery operates. Determine the balanced half-reactions, the overall redox reaction, and the anode and cathode in this galvanic cell. 

C19-0022. Using the appropriate values from Table 19-1. calculate E ° for one cell of a lead storage battery. (Six of these cells are connected in series in an automobile storage battery.)... 

The lead storage battery provides electrical power in automobiles. It is well suited for this use because it supplies the large current needed to drive starter motors and headlights and can be recharged easily. Figure 19-20 shows the lead storage cell in a schematic view. The half-reactions are the subject of Example ... 

The lead storage cell (six of which make up the lead storage battery commonly used in automobiles) will be discussed as an example of a practical cell. The cell, pictured in Fig. 14-2, consists of a lead electrode and a lead dioxide electrode immersed in relatively concentrated H2S04 in a single container. When the cell delivers power (when it is used), the electrodes react as follows ... 

In the lead storage battery, insoluble lead sulfate, PbS04(s), is produced at both the anode and cathode during cell discharge. 

Secondary cells are voltaic cells that can be recharged repeatedly. The lead storage battery and nickel-cadmium cell are examples of secondary cells. The lead storage battery consists of six voltaic cells. Its electrodes are lead alloy plates, which take the form of a grill, filled with spongy lead metal. The cathode consists of another group of plates filled with lead (IV) oxide, P6O2. Dilute sulfuric acid is the electrolyte of the cell. When the battery delivers a current, the lead is oxidized to lead ions, which combine with sulfate fS0 7 ions of the electrolyte to cover the lead electrode. 

The lead storage battery can be recharged by passing a direct current through the cell in the reverse direction. The electrical energy required to make this reaction happen is furnished by an alternator to convert alternating current to direct current The reverse reaction is as follows ... 

The initial current is usually 6-8 amperes at 50-60 volts. The resistance of the cell constantly changes because of depletion of electrolyte and deposition of potassium methoxide in the pores of the ceramic cup. The preferred source of current is a rectifier capable of delivering 10-15 amperes at 30-90 volts. Lead storage batteries connected in series are also satisfactory but require frequent recharging. 

FIGURE 18.8 A lead storage battery and a cutaway view of one cell. Each electrode consists of several grids with a large surface area so that the battery can deliver the high currents required to start an automobile engine. The electrolyte is aqueous sulfuric acid. 

Because the reaction product (solid PbS04) adheres to the surface of the electrodes, a "run-down" lead storage battery can be recharged by using an external source of direct current to drive the cell reaction in the reverse, nonspontaneous direction. In an automobile, the battery is continuously recharged by a device called an alternator, which is driven by the engine. 

The standard cell potential for a lead storage battery is 1.924 V. Calculate AG° (in kilojoules) for the cell reaction... 

The reducing and oxidizing agents in a standard electrochemical cell are depleted with time. In a rechargeable battery (e.g., lead storage batteries in cars) the direction of the spontaneous redox reaction is reversed and reactants are regenerated when electrical energy is added into the system. A fuel cell has the same components as a standard electrochemical cell except that reactants are continuously supplied. 

The lead storage cell, six of which constitute the lead storage battery, is familiar for its use in most automobiles. It will be described in some detail because it has several features that are different from those of the Daniell cell, described earlier. The lead storage cell (Figure 17.2) consists of a lead electrode coated with a paste of lead(II) sulfate and another electrode which has lead(IV) oxide as the active oxidizing agent, also coated with lead(II) sulfate. The electrolyte is concentrated sulfuric acid, in which PbS04 is insoluble. Both electrodes are situated in the same solution. The half-reactions are... 

One of the six cells in a 12-V lead storage battery. The anode consists of a lead grid filled with spongy lead, and the cathode is a lead grid filled with lead dioxide. The cell also contains 38% (by mass) sulfuric acid. 

Primary cells are cells like the ordinary dry cell that cannot be recharged. Storage cells are cells like the nickel-cadmium cell or the lead-storage battery that can be recharged. Is the Zn-Cu + cell shown above a primary cell or a storage cell ... 

Batteries vary in size and chemistry. Shown here are an automobile lead-storage battery, rechargeable nickel-cadmium cells, alkaline cells, and zinc-carbon dry cells. 

One technically important secondary battery is the lead-acid storage battery, used in automobiles. A 12-V lead storage battery consists of six 2.0-V cells (Fig. 17.9) connected in series (cathode to anode) by an internal lead linkage and housed in a hard rubber or plastic case. In each cell the anode consists of metallic lead in porous form to maximize its contact area with the electrolyte. The cathode is of similar design, but its lead has been converted to lead dioxide. A sulfuric acid solution (37% by mass) serves as the electrolyte. 

The E.M.F. of a lead storage battery containing 2.75 molal sulfuric acid was found to be 2.005 volt at 25 C. The aqueous vapor pressure of the acid solution at this temperature is about 20.4 mm., while that of pure water is 23.8 mm. The mean ionic activity coefficient of the sulfuric acid is 0.136. Calculate the standard free energy change of the cell reaction at 25 C and check the values from tabulated free energy data. 

The Lead Storage Battery 21-24 The Nickel-Cadmium (Nicad) Cell... 

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