Chemical energy/electrical

Since in the interconversion of electrical and chemical energies, electrical energy flows to or from the system in which chemical changes lake place, it is essential that the system be. in large part, conducting or consist of electrical conductors. These are of two general types—electronic and electrolytic—though some materials exhibit both types of conduction. Metals are the most common electronic conductors. Typical electrolytic conductors are molten salts and solutions of acids, bases, and salts. 

Primary batteries Chemical energy —> electrical energy Consumer appliances, portable devices, medical applications (low cost, high reliability)... 

Fuel cells Chemical energy —> electrical energy (continuous supply of gaseous components) Power plants Heat-power devices (efficient fuel conversion)... 

Electrochemical capacitors Chemical energy <= electrical energy High power density applications... 

Electrochemistry is concerned with the interconversion of electrical and chemical energy. Electrical effects occur as a result of the movement of electrical charge, either as mobile ions in an aqueous solution or melted liquid or as delocalized electrons in a conductor. Electrolytic and voltaic cells are the two types of electrochemical cells. 

Dethreading/rethreading of the wire and ring components of a pseudorotaxane reminds the movement of a piston in a cylinder. We have shown that, in - suitable pseudorotaxanes, the movement of such a rudimentary molecular machine can be feeded by chemical energy, electrical energy, or light. 

Chemical energy Electrical energy Thermal energy... 

Hydrogen use as a fuel in fuel cell appHcations is expected to increase. Fuel cells (qv) are devices which convert the chemical energy of a fuel and oxidant directiy into d-c electrical energy on a continuous basis, potentially approaching 100% efficiency. Large-scale (11 MW) phosphoric acid fuel cells have been commercially available since 1985 (276). Molten carbonate fuel cells (MCFCs) ate expected to be commercially available in the mid-1990s (277). 

Fuel Cell Catalysts. Euel cells (qv) are electrochemical devices that convert the chemical energy of a fuel direcdy into electrical and thermal energy. The fuel cell, an environmentally clean method of power generation (qv), is more efficient than most other energy conversion systems. The main by-product is pure water. 

In bulk chemical reactions, an oxidizer (electron acceptor) and fuel (electron donor) react to form products resulting in direct electron transfer and the release or absorption of energy as heat. By special arrangements of reactants in devices called batteries, it is possible to control the rate of reaction and to accomplish the direct release of chemical energy in the form of electricity on demand without intermediate processes. 

Batteries are miniatuie chemical leactois that convert chemical energy into electrical energy on demand. The thermodynamics of battery systems foUow direcdy from that for bulk chemical reactions (10). For the general reaction... 

Because batteries direcdy convert chemical energy to electrical energy ia an isothermal process, they are not limited by the Carnot efficiency. The thermodynamic efficiency S for electrochemical processes is given by ... 

R. H. SchaUenberg, Bottled Energy Electrical Engineering and the Evolution of Chemical Energy Storage, American Philosophical Society, Philadelphia, Pa., 1982. 

Electrochemical systems convert chemical and electrical energy through charge-transfer reactions. These reactions occur at the interface between two phases. Consequendy, an electrochemical ceU contains multiple phases, and surface phenomena are important. Electrochemical processes are sometimes divided into two categories electrolytic, where energy is supplied to the system, eg, the electrolysis of water and the production of aluminum and galvanic, where electrical energy is obtained from the system, eg, batteries (qv) and fuel cells (qv). 

In some instances, however, pai t of the chemical energy bound in relatively high-enthalpy compounds can be converted directly to electricity as these reactants are converted to produc ts of lower enthalpy (galvanic action). A process in the opposite direc tion also is possible for some systems an elec tric current can be absorbed as the increased chemical energy of the higher-enthalpy compounds (electrolytic action). The devices in which electrochemical energy conversion processes occur are called cells. 

An explosion is defined by StrelUow and Baker " as an event in wliich energy is released over a sufficiently small period of time and in a sufficiently small volmne to generate a pressure wave of finite amplitude traveling away from tlie source. Tliis energy may have been originally stored in tlie system as chemical, nuclear, electrical, or pressure energy. However, tlie release is not considered to be explosive unless it is rapid and concentrated enough to produce a pressure wave tliat can be heard. 

A battery is a series of electrochemical cells. Electrochemical cells are devices that, whenever in use, can continuously and directly convert chemical energy into electrical energy. 

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