Chemistry
Electrolysis
Electrolysis is a chemical process that uses an electric current to drive a non-spontaneous chemical reaction. It involves the decomposition of a compound into its elements or simpler compounds at the electrodes. This process is commonly used in various industrial applications, such as the production of metals and the purification of elements.
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eBook - PDFElectrochemical Methods
Fundamentals and Applications
- Allen J. Bard, Larry R. Faulkner(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
C H A P T E R 1 INTRODUCTION AND OVERVIEW OF ELECTRODE PROCESSES 1.1 INTRODUCTION Electrochemistry is the branch of chemistry concerned with the interrelation of electri- cal and chemical effects. A large part of this field deals with the study of chemical changes caused by the passage of an electric current and the production of electrical en- ergy by chemical reactions. In fact, the field of electrochemistry encompasses a huge array of different phenomena (e.g., electrophoresis and corrosion), devices (elec- trochromic displays, electroanalytical sensors, batteries, and fuel cells), and technolo- gies (the electroplating of metals and the large-scale production of aluminum and chlorine). While the basic principles of electrochemistry discussed in this text apply to all of these, the main emphasis here is on the application of electrochemical methods to the study of chemical systems. Scientists make electrochemical measurements on chemical systems for a variety of reasons. They may be interested in obtaining thermodynamic data about a reaction. They may want to generate an unstable intermediate such as a radical ion and study its rate of decay or its spectroscopic properties. They may seek to analyze a solution for trace amounts of metal ions or organic species. In these examples, electrochemical methods are employed as tools in the study of chemical systems in just the way that spectroscopic methods are frequently applied. There are also investigations in which the electrochemi- cal properties of the systems themselves are of primary interest, for example, in the design of a new power source or for the electrosynthesis of some product. Many electrochemical methods have been devised. Their application requires an understanding of the fundamen- tal principles of electrode reactions and the electrical properties of electrode–solution in- terfaces. In this chapter, the terms and concepts employed in describing electrode reactions are introduced.
eBook - PDF- Leslie Basford(Author)
- 2013(Publication Date)
- Made Simple(Publisher)
Solutions of acids, bases, and salts are called electrolytes; they can conduct electricity because they contain charged ions. In Electrolysis the negatively charged electrode is called the cathode and the positively charged electrode is the anode. In the electroplating process material dissolved from the anode is deposited on the cathode. Faraday's laws of Electrolysis state: (i) the weight of any material liberated by Electrolysis is directly proportional to the quantity of charge passing (i.e. to the product of current x time); (ii) 96,500 coulombs of charge liberates the equivalent weight (Le. atomic weight -7-valency) in grams of any chemical element. If n identical cells are connected in series the total e.m.f. is n times that of a single cell; if they are connected in parallel the total e.m.f. is equal to that of a single cell, but the combination can deliver a current n times as great as that from a single cell. All cells convert chemical energy into electrical energy. In the simple cell electrical energy is produced when zinc dissolves in sulphuric acid. The e.m.f. of a cell can be predicted from the difference between the electrode potentials of its two plates. The simple cell suffers from polarization, i.e. the accumulation of hydrogen on its positive plate; this is overcome in practical cells by the addition of a depolarizing chemical which converts hydrogen to water. Storage batteries can be recharged when their chemical energy is exhausted. This is achieved by passing a current through the battery to reverse the reactions that have taken place during discharge.
eBook - PDFFuel Cells
Principles, Design, and Analysis
- Shripad T. Revankar, Pradip Majumdar(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
33 2 Review of Electrochemistry Electrochemistry is the study of mutual transformation of chemical and elec-trical energy. Specifically, it deals with chemical reactions driven by an electric current and with the electricity produced by chemical reactions. Examples of electrochemistry are electroplating, iron oxidation (rusting), solar-energy conversion, electrochemical conversions (fuel cells, batteries), photosynthe-sis, and respiration. In this chapter, the principles of electrochemistry are reviewed. First, let us briefly look into the history of electrochemistry. The field of electrochemistry was discovered near the beginning of the 19th century. In 1791, Italian physician and anatomist Luigi Galvani observed that while dissecting a frog, a coworker touched the internal cru-ral nerves of the frog with the tip of a scalpel and all the muscles of the frog’s limb contracted. This led him to establish a relation between chemical reactions and electricity. In 1880, Alessandro Volta reported on chemical-to-electrical energy conversion to the Royal Society in London. He showed that by placing a brine-soaked membrane in contact with silver and zinc plates, on either side, an electric current would flow in the external circuit connecting the silver and zinc plates. Volta is credited with building the first electrochemical cell, which consisted of two electrodes: one made of zinc, the other of copper and the electrolyte is sulfuric acid or a brine mixture of salt and water. Following this, the same year William Nicholson and Johann Wilhelm Ritter succeeded in decomposing water into hydrogen and oxy-gen by Electrolysis (electricity to chemicals). Further work on Electrolysis by Sir Humphry Davy led to the conclusion that the production of electricity in simple electrolytic cells resulted from chemical action and that chemi-cal combination occurred between substances of opposite charge.
eBook - PDFElectrical Installation Work: Level 2
EAL Edition
- Trevor Linsley(Author)
- 2019(Publication Date)
- Routledge(Publisher)
The conductors which make contact with the Defnition When an electric current fows in a circuit it can have one or more of the following three effects: heating, magnetic or chemical . 110 EAL Electrical Installation Work Level 2 2 liquid are called the anode and cathode. The liquid itself is called the electrolyte, and the process is called Electrolysis . Electrolysis is an industrial process used in the refning of metals and electroplating. It was one of the earliest industrial applications of electric current. Most of the aluminium produced today is extracted from its ore by electrochemical methods. Electroplating serves a double purpose by protecting a base metal from atmospheric erosion and also giving it a more expensive and attractive appearance. Silver and nickel plating has long been used to enhance the appearance of cutlery, candlesticks and sporting trophies. An anode and cathode of dissimilar metal placed in an electrolyte can react chemically and produce an e.m.f. When a load is connected across the anode and cathode, a current is drawn from this arrangement, which is called a cell. A battery is made up of a number of cells. It has many useful applications in providing portable electrical power, but electrochemical action can also be undesirable since it is the basis of electrochemical corrosion which rots our motor cars, industrial containers and bridges. When a load such as a light bulb is connected across the battery, the circuit is complete and a chemical reaction occurs which breaks down the electrolyte and then deposits positive ions on one plate and negative electrons on the other. This then creates a fow of electrical energy in the device, in this case lighting up the lamp. Any voltage that is created is known as an e.m.f. (electromotive force). Figure 2.12 It takes a chemical reaction to turn this light bulb on. A battery is a sequence or collection of cells and there are two types of battery in general use: primary and secondary cells.
eBook - PDF- D Pletcher, R Greff, R Peat, L M Peter, J Robinson(Authors)
- 2001(Publication Date)
- Woodhead Publishing(Publisher)
1.1 — Schematic view of some types of electrode reactions met in applied and fundamental electrochemistry. 18 Introduction to the fundamental concepts of electrochemistry [Ch. 1 Electrolysis is only possible in a cell with both an anode and a cathode, and, because of the need to maintain an overall charge balance, the amount of reduction at the cathode and oxidation at the anode must be equal. The total chemical change is found by adding the two individual electrode reactions; for example, the chemical change in a chlor-alkali membrane or diaphragm cell is obtained by adding Equations (1.3) and (1.8), i.e. 2CP+ 2H 2 0 -> Cl 2 + H 2 + 20H~ . (1.11) Moreover, when Electrolysis occurs, in addition to electron transfer at the anode and cathode surfaces, ions must pass through the solution between the electrodes and electrons though the wires externally interconnecting the two electrodes (in order to maintain electrical neutrality at all points in the system). Hence the current through the external circuit, /, given by / = AI (1.12) (when A is the electrode area and / the current density), is a convenient measure of the rate of the cell reaction, and the charge, q, passed during a period, f, indicates the total amount of chemical reaction which can have taken place: indeed, the charge required to convert m moles of starting material to product in an electrode reaction involving the transfer of n electrons/molecule is readily calculated using Faraday's law rt q = I idt = mnF . (1.13) Jo When the two electrodes of a cell are interconnected by an external circuit, however, the cell reaction will only occur spontaneously if the free energy change associated with the net cell reaction is negative. This is not the case in a cell for the production of chlorine and caustic soda, i.e. the free energy of reaction (1.11) is positive, and for reaction (1.11) to occur it will be necessary to supply energy by applying a potential between the two electrodes. This potential must certainly be
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
19.7 Electrolytic Cells 971 FIGURE 19.16 Diagram of the internal parts of a photovoltaic cell. a. Glass protective covering, b. antireflective coating, c. electrode mesh, d. n-type semiconductor material, e. p-type semiconductor material, f. electrode. The thickness of this cell is approximately 0.3 mm, and the n-type semiconductor is approximately 0.002 mm thick. FIGURE 19.17 Acres of photovoltaic cells can produce large amounts of energy. Stocktrek Images/Getty Images a b c d e Sunlight f 19.7 Electrolytic Cells In our preceding discussions, we’ve examined how spontaneous redox reactions can be used to generate electrical energy. We now turn our attention to the opposite process, the use of electrical energy to force nonspontaneous redox reactions to occur. When electricity is passed through a molten (melted) ionic compound or through a solu- tion of an electrolyte, a chemical reaction occurs that we call Electrolysis. A typical electroly- sis apparatus, called an Electrolysis cell or electrolytic cell, is shown in Figure 19.18. This particular cell contains molten sodium chloride. (A substance undergoing Electrolysis must be molten or in solution so its ions can move freely and conduction can occur.) Inertelectrodes— electrodes that won’t react with the molten NaCl or the Electrolysis products—are dipped into the cell and then connected to a source of direct current (DC) electricity. The DC source serves as an “electron pump,” pulling electrons away from one electrode and pushing them through the external wiring onto the other electrode. The electrode from which electrons are removed becomes positively charged, while the other electrode becomes negatively charged. When electricity starts to flow, chemical changes begin to happen. At the positive electrode, oxidation occurs as electrons are pulled away from negatively charged chloride ions. Because of the nature of the chemical change, therefore, thepositiveelectrode becomestheanode.
eBook - PDFElectrolytes
Supramolecular Interactions and Non-Equilibrium Phenomena in Concentrated Solutions
- Georgii Georgievich Aseyev(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
The energy of that heat motion is not usually enough in order to overcome chemical attractive forces holding oppositely charged parts of a molecule together. In solutions, however, forces of chemical affinity are weakened under the influence of the solvent, and a molecule, at least, for a short period of time dissociates , that is, decomposes into oppositely charged ions. In case a positive ion meets with a negative one, ions may recombine , that is, get connected into a neutral molecule. Other neutral molecules, vice versa, may dissociate into ions. As a result of continu-ous processes of dissociation and recombination, statistical equilibrium is set where a fraction of dissociated molecules stays in average over time. By applying the elec-tric field, positive and negative ions start rushing in opposite directions according to the views of Grotthuss. The electric current appears and liberation of decomposition products takes place on electrodes. Thus, the electric field has nothing to do with chemical decomposition of solute molecules into component elements. The role of the electric field only comes down to separation of already existing positive and negative ions and collecting them on different electrodes. This is the essence of the Electrolysis phenomenon. 206 Electrolytes In the history of chemistry during the 1870s–1880s, it is the period when the struggle for the theory of chemical composition, for specifying the notions of atom , molecule , and ion , was still on track, which interfered with the understanding of the electrolyte electrical conductivity mechanism. F.G. Kohlrausch performed a series of works in the field of physicochemistry of solutions and promoted understanding of the ion nature. In 1879, he discovered independence of ion motion in electrolytes at infinite dilution and formulated the electrical conductivity additivity law (Kohlrausch’s law).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
_________________________ WORLD TECHNOLOGIES _________________________ Chapter 11 Electrochemistry English chemists John Daniell (left) and Michael Faraday (right), both credited as founders of electrochemistry today. Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution. If a chemical reaction is driven by an external applied voltage, as in Electrolysis, or if a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. In contrast, chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and reduction reactions are separated in space or time, connected by an external electric circuit to understand each process. _________________________ WORLD TECHNOLOGIES _________________________ History 16th to 18th century developments German physicist Otto von Guericke beside his electrical generator while conducting an experiment. Understanding of electrical matters began in the sixteenth century. During this century the English scientist William Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gilbert became known as the Father of Magnetism. He discovered various methods for producing and strengthening magnets. In 1663 the German physicist Otto von Guericke created the first electric generator, which produced static electricity by applying friction in the machine. The generator was made of a large sulfur ball cast inside a glass globe, mounted on a shaft. The ball was rotated by means of a crank and a static electric spark was produced when a pad was rubbed against the ball as it rotated.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter 2 Electrochemistry English chemists John Daniell (left) and Michael Faraday (right), both credited as founders of electrochemistry today. Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution. If a chemical reaction is driven by an external applied voltage, as in Electrolysis, or if a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. In contrast, chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and reduction reactions are separated in space or time, connected by an external electric circuit to understand each process. ____________________ WORLD TECHNOLOGIES ____________________ History 16th to 18th century developments German physicist Otto von Guericke beside his electrical generator while conducting an experiment. Understanding of electrical matters began in the sixteenth century. During this century the English scientist William Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gilbert became known as the Father of Magnetism. He discovered various methods for producing and strengthening magnets. In 1663 the German physicist Otto von Guericke created the first electric generator, which produced static electricity by applying friction in the machine. The generator was made of a large sulfur ball cast inside a glass globe, mounted on a shaft. The ball was rotated by means of a crank and a static electric spark was produced when a pad was rubbed against the ball as it rotated.
eBook - PDFAn Introduction to Chemical Metallurgy
International Series on Materials Science and Technology
- R. H. Parker, D. W. Hopkins(Authors)
- 2016(Publication Date)
- Pergamon(Publisher)
CHAPTER 5 Electrochemistry 5.1. Introduction In an electronic conductor, an electric current is the result of a net movement of electrons in the structure of the con-ductor when an electrical potential is applied. Electrons have negligible mass compared with the remainder of the structure, and the flow of electricity is not accompanied by a significant movement of matter. Electrolytic conductors contain mobile ions, which carry an electrical charge. When an electrical potential is applied, these ions will move in the direction appropriate to their charge. As in electronic con-ductance, the electric current is a movement of electrical charge, but this time the charge is carried by ions of significant mass and electrolytic conductance is accompanied by mass transfer. Conductors may exhibit a combination of electronic and electrolytic conduction, but frequently the propor-tion of one type is so dominating that it is permissible to assume that the conduction is entirely by the dominating mechanism. This property of electrolytic conduction plays a major role in some of the processes and phenomena important to the metallurgist—corrosion and oxidation of metals, electro-plating, electropolishing, electrolytic extraction and refining of metals, for example. We will first consider the nature of electrolytes and electrolytic conductance, and then their function in galvanic cells and Electrolysis. Some metallurgical applications will be considered in more detail in later chapters (7 and 8). 159 160 AN INTRODUCTION TO CHEMICAL METALLURGY 5.2. Electrolytes The most detailed study of electrolytes (an alternative name for electrolytic conductors) has been carried out on aqueous solutions, but fused salts and solids can also be of considerable importance as electrolytic conductors. If we consider a crystalline solid, the salt MX, whose bond-ing is ionic (electrovalent) in character, the structure will consist of a lattice of ions M + and X~ (Fig. 5.1).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Research World(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 5 Electrochemistry English chemists John Daniell (left) and Michael Faraday (right), both credited as founders of electrochemistry today. Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution. If a chemical reaction is driven by an external applied voltage, as in Electrolysis, or if a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. In contrast, chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and reduction reactions are separated in space or time, connected by an external electric circuit to understand each process. ________________________ WORLD TECHNOLOGIES ________________________ History 16th to 18th century developments German physicist Otto von Guericke beside his electrical generator while condu cting an experiment. Understanding of electrical matters began in the sixteenth century. During this century the English scientist William Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gi lbert became known as the Father of Magnetism. He discovered various methods for producing and strengthening magnets. In 1663 the German physicist Otto von Guericke created the first electric generator, which produced static electricity by applying friction in the machine. The generator was made of a large sulfur ball cast inside a glass globe, mounted on a shaft. The ball was rotated by means of a crank and a static electric spark was produced when a pad was rubbed against the ball as it rotated.
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