Batteries free energy

In considering the selection of anodes for high energy density (HED) storage (or secondary) batteries (SB), we note that there are some 19 metals whose free-energy density (TED) of reaction with oxidants such as O2, Cl2, and F2 are higher than those of Zn with the same oxidants. Most of these metals react violently with water. The remainder are passivated by water. Therefore other electrolytes must be considered for these metals, based on non-aqueous, molten salt, or solid-state ionic conductors. Much experimental work has been carried out during the last two decades on primary and secondary batteries based on anhydrous electrolytes, aimed at utilization of the active metals. 

Terms. TED - theoretical energy density (free energy of reaction/sum of molar wts of reactants) ED practical or realized Wh/kg SB - secondary or storage battery (rechargeable) dod - depth of discharge (% recharge removed before recharge) ... 

The E°cell of an aluminium-air battery is 2.73 volts and it involves all electron process. The free energy change (DG°) of the battery in kJ. Calculated ... 

Most environmental conditions do not allow for calculation of these potentials at 25°C in this case, temperature effects cannot be easily neglected. We aU know that a car battery has less cranking power on a cold winter morning than it does on a warm snmmer day. Temperatnre effects can be taken into account by returning to the free energy, which already accounts for temperatnre fluctuations. Equation (3.8) developed at the beginning of this chapter is where we start. 

The change in standard free energy is -50,800 cal/mole whether metallic Zn is wastefully put into a beaker of CuS04 or whether the reaction is usefully employed as a battery as in Figure 17-1. Either way, the products end up being less capable of doing work than they were before starting the reaction. 

Gibbs free energy - ENGINEERING, CHEMICALDATA CORRELATION] (Vol 9) -for battery systems [BATTERIES - INTRODUCTION] (Vol 3) -of electron transfer [PHOTOCHEMICAL TECHNOLOGY - SURVEY] (Vol 18)... 

We now see that mitochondria contain a variety of molecules—cytochromes, flavins, ubiquinone, and iron-sulfur proteins—all of which can act as electron carriers. To discuss how these carriers cooperate to transport electrons from reduced substrates to 02, it is useful to have a measure of each molecule s tendency to release or accept electrons. The standard redox potential, E°, provides such a measure. Redox potentials are thermodynamic properties that depend on the differences in free energy between the oxidized and reduced forms of a molecule. Like the electric potentials that govern electron flow from one pole of a battery to another, E° values are specified in volts. Because electron-transfer reactions frequently involve protons also, an additional symbol is used to indicate that an E° value applies to a particular pH thus, E° refers to an E° at pH 7. 

The silver oxide-zinc battery used in hearing aids delivers a voltage of 1.60 V. Calculate the free-energy change (in kilojoules) for the cell reaction... 

Manufacturing-Power Supplies Battery-Free Back-Up Power Systems Flywheel Energy Systems... 

One of the oldest and most important applications of electrochemistry is to the storage and conversion of energy. You already know that a galvanic cell converts chemical energy to work similarly, an electrolytic cell converts electrical work into chemical free energy. Devices that carry these conversions out on a practical scale are called batteries1. In ordinary batteries the chemical components are contained within the device itself. If the reac-tantsare supplied from an external source as they are consumed, the device is called a fuel cell. 

The words, fuel cells and batteries, lead to the misconception that there must be a close connection between the two devices. However, the connection is only apparent and the purpose of each device is utterly different. The fuel cell is an electrical energy producer (Sec. 7.1.3.2) one takes a fuel (e.g., methanol) and leads it into the oxidizing anode of a fuel cell. At the counter-cathode, oxygen in air is reduced. The free energy of the oxidation of, for example, methanol comes out not as heat (as it would in a chemical engine), but directly as electrical energy. So fuel cells produce electricity. They should be called electrochemical electricity producers (eces), although that s perhaps too much of a mouthful. 

Calculate the free energy change (heat change) of the cell reaction (AH) in calories for two battery systems (a) A lead-acid cell with an open-circuit voltage of 2.01 V at 15 °C and a temperature coefficient of resistance (dE/dT) of 0.0037 V/K. (b) A Zn-Hg cell (Clark cell) with an open-circuit potential of 1.4324 V at 15 °C and a temperature coefficient of 0.00019 V/K. (Bhardwaj)... 

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