Electric current reactions

Expt. Al dissolved Mean Electrical Current Reaction C4H2 pressure Oils Polyethylene... 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Protonic initiation is also the end result of a large number of other initiating systems. Strong acids are generated in situ by a variety of different chemistries (6). These include initiation by carbenium ions, eg, trityl or diazonium salts (151) by an electric current in the presence of a quartenary ammonium salt (152) by halonium, triaryl sulfonium, and triaryl selenonium salts with uv irradiation (153—155) by mercuric perchlorate, nitrosyl hexafluorophosphate, or nitryl hexafluorophosphate (156) and by interaction of free radicals with certain metal salts (157). Reports of "new" initiating systems are often the result of such secondary reactions. Other reports suggest standard polymerization processes with perhaps novel anions. These latter include (Tf)4Al (158) heteropoly acids, eg, tungstophosphate anion (159,160) transition-metal-based systems, eg, Pt (161) or rare earths (162) and numerous systems based on tri flic acid (158,163—166). Coordination polymerization of THF may be in a different class (167). 

Electrochemical Process. Applying an electrical current to a brine solution containing propylene results in oxidation of propylene to propylene oxide. The chemistry is essentially the same as for the halohydrin process. AH of the chemistry takes place in one reactor. Most of the reported work uses sodium or potassium bromide as the electrolyte. Bromine, generated from bromide ions at the anode, reacts with propylene and water to form propylene bromohydrin. Hydroxide generated at the cathode then reacts with the bromohydrin to yield propylene oxide (217—219). The net reaction involves transfer of two electrons ... 

Jictive mass is the material which generates electrical current by means of a chemical reaction within the battery. 

The term electrochromism was apparently coined to describe absorption line shifts induced in dyes by strong electric fields (1). This definition of electrocbromism does not, however, fit within the modem sense of the word. Electrochromism is a reversible and visible change in transmittance and/or reflectance that is associated with an electrochemicaHy induced oxidation—reduction reaction. This optical change is effected by a small electric current at low d-c potential. The potential is usually on the order of 1 V, and the electrochromic material sometimes exhibits good open-circuit memory. Unlike the well-known electrolytic coloration in alkaU haUde crystals, the electrochromic optical density change is often appreciable at ordinary temperatures. 

Galvanic cells in which stored chemicals can be reacted on demand to produce an electric current are termed primaiy cells. The discharging reac tion is irreversible and the contents, once exhausted, must be replaced or the cell discarded. Examples are the dry cells that activate small appliances. In some galvanic cells (called secondaiy cells), however, the reaction is reversible that is, application of an elec trical potential across the electrodes in the opposite direc tion will restore the reactants to their high-enthalpy state. Examples are rechargeable batteries for household appliances, automobiles, and many industrial applications. Electrolytic cells are the reactors upon which the electrochemical process, elec troplating, and electrowinning industries are based. 

This handbook deals only with systems involving metallic materials and electrolytes. Both partners to the reaction are conductors. In corrosion reactions a partial electrochemical step occurs that is influenced by electrical variables. These include the electric current I flowing through the metal/electrolyte phase boundary, and the potential difference A( = 0, - arising at the interface. and represent the electric potentials of the partners to the reaction immediately at the interface. The potential difference A0 is not directly measurable. Therefore, instead the voltage U of the cell Me /metal/electrolyte/reference electrode/Me is measured as the conventional electrode potential of the metal. The connection to the voltmeter is made of the same conductor metal Me. The potential difference - 0 is negligibly small then since A0g = 0b - 0ei ... 

Stray current corrosion is an electrolytic degradation of a metal caused by unintentional electrical currents. Bad grounds are the most prevalent causes. The corrosion is actually a typical electrolysis reaction. 

Electrolysis-a reaction in which chemical change results in an electrolyte being produced from the passage of electric current. 

The chemical process that produces an electrical current from chemical energy is called an oxidation-reduction reaction. The oxidation-reduction reaction in a battery involves the loss of electrons by one compound (oxidation) and the gain of electrons (reduction) by another compound. Electrons are released from one part of the batteiy and the external circuit allows the electrons to flow from that part to another part of the batteiy. In any battery, current flows from the anode to the cathode. The anode is the electrode where positive current enters the device, which means it releases electrons to the external circuit. The cathode, or positive terminal of the battery, is where positive current leaves the device, which means this is where external electrons are taken from the external circuit. 

To exploit the energy produced in this reaction, the half reactions are separated. The oxidation reaction is carried out at a zinc electrode (Zn Zir + 2 electrons) and the reduction reaction is carried out at a copper electrode (Cu"" + 2 electrons Cu metal). Electrons flow through a metal wire from the oxidizing electrode (anode) to the reducing electrode (cathode), creating electric current that can be harnessed, for example, to light a tungsten bulb. 

A voltaic cell using this reaction is similar to the Zn-Cu2+ cell the Zn Zn2+ half-cell and the salt bridge are the same. Because no metal is involved in the cathode half-reaction, an inert electrode that conducts an electric current is used. Frequently, the cathode is made of platinum (Figure 18.3, p. 484). In the cathode, Co3+ ions are provided by a solution of Co(N03)3. The half-reactions occurring in the cell are... 

Calcium chloride, CaCl2, is another crystalline solid that dissolves readily in water. The resulting solution conducts electric current, as does the sodium chloride solution. Calcium chloride is, in this regard, like sodium chloride and unlike sugar. The equation for the reaction is... 

All the hydrogen halides are gaseous at room temperature but hydrogen fluoride liquefies at 19.9°C and 1 atmosphere pressure. The most important chemistry of the hydrogen halides relates to their aqueous solutions. All of the hydrogen halides dissolve in water to give solutions that conduct electric current, suggesting that ions are present. The reactions may be written ... 

Figure 7-5 shows an apparatus in which an electric current can be passed through water. As remarked in Section 3-1.2, the electric current causes a decomposition of water. As work is done (electrical work), hydrogen gas and oxygen gas are produced. Measurements of the electric current and voltage show that 68.3 kcal of electrical work, W, must be done to decompose one mole of water. The equation for the reaction is... 

A typical example is as follows. Benzoic acid, C6H5COOH, is a solid substance with only moderate solubility in water. The aqueous solutions conduct electric current and have the other properties of an acid listed in Section 11-2.1. We can describe this behavior with reaction (42) leading to the equilibrium relation (43) ... 

Electrochemical cells are familiar—a flashlight operates on current drawn from electrochemical cells called dry cells, and automobiles are started with the aid of a battery, a set of electrochemical cells in tandem. The last time you changed the dry cells in a flashlight because the old ones were dead, did you wonder what had happened inside those cells Why does electric current flow from a new dry cell but not from one that has been used many hours We shall see that this is an important question in chemistry. By studying the chemical reactions that occur in an electrochemical cell we discover a basis for predicting whether equilibrium in a chemical reaction fa-... 

These ideas, developed for an electrochemical cell, have great importance in chemistry because they are also applicable to chemical reactions that occur in a single beaker. Without an electric circuit or an opportunity for electric current to flow, the chemical changes that occur in a cell can be duplicated in a single solution. It is reasonable to apply the same explanation. 

So far in this chapter we have dealt with reactions that proceed spontaneously. But the same ideas and names are applied to reactions that we force to take place, against their natural tendency, by supplying energy with an externally applied electric current. Such a process is termed electrolysis or separation by electricity. ... 

In order to make Na(s) and C 2(g), an electric current is passed through NaClfiJ. What does the energy supplied to this reaction do ... 

Electrochemical power sources convert chemical energy into electrical energy. At least two reaction partners undergo a chemical process during operation. The energy of this reaction is available as electric current at a defined voltage and time [1]. 

Under most conditions, the process is spontaneous/ A chemical potential difference drives the reaction and AG < 0. When the reactants are separated as shown in Figure 9.3, the chemical potential difference can be converted to an electrical potential E. When the electrodes are connected through an external circuit, the electrical potential causes an electric current to flow. Because the electrical potential is the driving force for electrons to flow, it is sometimes... 

Figure 1.4. Possible pathways of 0(a) and Na(a) adsorbed species created at the three-phase boundaries via application of electric current (a) Desorption (b) Reaction (c) Backspillover.

How can a spontaneous reaction can be used to generate an electric current To find the answer, consider the redox reaction between zinc metal and copper(II) ions ... 

---