Chemistry
Redox Reactions
Redox reactions involve the transfer of electrons between chemical species. The substance that loses electrons is oxidized, while the one that gains electrons is reduced. These reactions are fundamental in various chemical processes, including energy production, corrosion, and industrial synthesis.
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9 Key excerpts on "Redox Reactions"
eBook - PDFFoundations of Chemistry
An Introductory Course for Science Students
- Philippa B. Cranwell, Elizabeth M. Page(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
5 Oxidation-reduction (redox) reactions At the end of this chapter, students should be able to: • Understand that the processes of oxidation and reduction involve the transfer of electrons • Determine the oxidation numbers of elements in common chemical compounds • Write redox half-equations for oxidation and reduction reactions, and balance half-equations to obtain an overall equation for the redox reaction • Understand the action of oxidising and reducing agents in terms of elec-tron transfer • Use information from redox titrations to calculate concentrations and other relevant data about reacting species • Recognise disproportionation reactions and identify the redox processes involved 5.1 Redox Reactions 5.1.1 Electron transfer in Redox Reactions The term redox is composed from the two words reduction and oxidation . Oxidation and reduction reactions involve the transfer of electrons. In fact, most chemical reactions occur with the transfer of electrons. As we have seen in Chapter 2, elements react together to attain a more stable arrangement of outer electrons. Foundations of Chemistry: An Introductory Course for Science Students , First Edition. Philippa B. Cranwell and Elizabeth M. Page. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/Cranwell/Foundations Oxidation and reduction reactions were previously thought to involve the gain or loss of oxygen. When an element combines with oxygen, such as the reac-tion of magnesium ribbon in oxygen to form magnesium oxide, it is said to be oxidised . The equation for this reaction is 2Mg s + O 2 g 2MgO s The chemical opposite of oxidation is reduction, which was originally defined as the removal of oxygen. Often this chemical process is brought about by hydrogen, which can combine with oxygen to produce water.
eBook - PDF- Geoffrey M. Bowers, Ruth A. Bowers(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
61 chapter three Oxidation and reduction Cars are subject to (or take advantage of) oxidation/reduction (REDOX) reactions—reactions where electrons are transferred between chemical species—every day. Several examples of important Redox Reactions in cars include the combustion process in fossil fuel-burning engines, the electrochemistry involved in batteries and fuel cells, and the corrosion of metal car components. Because Redox Reactions always involve a trans-fer of electrons, REDOX chemistry may be used to generate a current, as in a battery, or be a relatively unnoticed aspect of a chemical reaction, as it often is in combustion or corrosion processes. REDOX chemistry is also essential to metal plating and corrosion protection in vehicles. In this chapter, we will focus on understanding the details of these automotive applications of REDOX chemistry. 3.1 A second look at combustion Chemistry Concepts : oxidation numbers, REDOX terminology, activity series Expected Learning Outcomes : • Explain basic REDOX terminology • Identify what is being oxidized and reduced in a combustion reaction In every REDOX process, some element or chemical component gains electrons from another element or chemical component in the system. The species that loses electrons is said to be oxidized and the species that gains electrons reduced , and a REDOX reaction always involves both oxidation and reduction. The origin of these terms relates to the chemical concept of oxidation numbers, which is a numerical system to track the flow of electrons in a chemical reaction, assuming that any electron trans-fer is complete. In other words, partial charges are not allowed. In most cases, the oxidation number of an ion is identical to its ideal charge in a particular substance, though the transition metals and many nonmet-als often have several possible oxidation states at most temperatures and pressures.
- Peter V. Hobbs(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
6 Oxidation-reduction reactions 6.1 Some definitions In Chapter 5 we saw that, in terms of the Br0nsted-Lowry theory, acid-base reactions involve proton transfer. Another large and impor-tant group of chemical reactions, particularly in aqueous solutions, involves electron transfer; these are referred to as oxidation-reduction (or redox) reactions. Redox Reactions are involved (1) in photosyn-thesis, which releases oxygen into the Earth's atmosphere; (2) in the combustion of fuels, which is responsible for rising concentrations of atmospheric carbon dioxide; (3) in the formation of acid precipitation; and (4) in many chemical reactions in Earth sediments. Oxidation refers to a loss of electrons, and reduction to a gain of electrons. For example, an oxidation reaction is Cu(s)->Cu 2+ (aq) + 2e-(6.1) where the symbol e~ indicates one free electron (which carries one unit of negative charge). A reduction reaction is 2Ag + (aq) + 2e-^2Ag(s) (6.2) Since electrons cannot be lost or gained overall, oxidation must always be accompanied by reduction. Thus, Eqs. (6.1) and (6.2) together form a redox reaction Cu(s) + 2Ag + (aq) -> Cu 2+ (aq) + 2Ag(s) (6.3) Equation (6.1) is called the oxidation half-reaction and Eq. (6.2) the reduction half-reaction for the overall reaction Eq. (6.3). If substance A causes the oxidation of substance B, substance A is called the oxidizing agent or oxidant. Thus, in Eq. (6.3), Ag + (aq) is the oxidant, because it causes Cu(s) to lose electrons (note that the oxidant 104 Oxidation numbers 105 is reduced, that is, it gains electrons). Similarly, if a substance A causes the reduction of substance B, substance A is called the reducing agent or reductant. In Eq. (6.3) Cu(s) is the reductant, because it causes Ag + (aq) to gain electrons (note that the reductant is oxidized, that is, it loses electrons).
eBook - PDF- Ramesh Chandra, Snigdha Singh, Aarushi Singh(Authors)
- 2020(Publication Date)
- Arcler Press(Publisher)
2CuO + C →2Cu + CO 2 Oxidation and Reduction reactions can be recognized with the gain and loss of oxygen. However, there is a wide definition of the oxidation and reduction reactions other than this. Oxidation and Reduction 177 In the beginning of the chemistry subject, the importance of oxidation-Re-duction reactions was recognized. In the oxidation-reduction reaction, there is a give and take of some entity in the two reacting chemicals. This forms the same basis for the acid-base reactions. Thus, in the chapter, there is a common feature that is shared by the acid-base and oxidation-reduction re-actions. Gradually, there has been the development of the important concepts of the reactions, for example, the oxidation number, an oxidant (an oxidizing agent), a reductant (a reducing agent), electromotive force, Nernst’s equation, Faraday’s law of electromagnetic induction, and electrolysis. A Reducing Agent reduces other substances and loses electrons; therefore, its oxi-dation state increases. An Oxidizing Agent oxidizes other substances and gains electrons; therefore, its oxidation state decrease. Among the concepts, the development of electric cells was significant. There is a satisfying intellectual challenge in assembling the components of the oxidation and reduction reactions. Two examples of such challenge are cells and electrolysis as both are strongly related in the everyday life and the chemical industry. 6.2. THE CONCEPTS OF OXIDATION-REDUCTION 6.2.1. Discovery of Oxygen There are substantial amounts of oxygen present in the air. The combination between substances and oxygen, i.e., oxidation, occurs most frequently in the reactions. In ancient times, the people came across combustion and rusting of the metals. The nature of combustion can be known only after knowing the nature of the oxygen. However, until the end of 18 th century, the chemists were not able to understand the true nature of the combustion.
- Olcay Tunay, Isik Kabdasli, Idil Arslan-Alaton, Tugba Olmez-Hanci(Authors)
- 2010(Publication Date)
- IWA Publishing(Publisher)
© 2010 IWA Publishing. Chemical Oxidation Applications for Industrial Wastewaters . By Olcay Tünay, Işık Kabdaşlı, Idil Arslan-Alaton and Tuğba Ölmez-Hancı . ISBN: 9781843393078. Published by IWA Publishing, London, UK. Chapter 1 Introduction to Redox Reactions 1.1 INTRODUCTION 1.1.1 Redox processes Chemical oxidation is a process in which the oxidation state of an atom is increased. The atom being oxidised may be in the elemental form or in a substance like a molecule or ion. The term “oxidised” is also used for the substance containing the oxidised atom. If the oxidation takes place within biological processes the terms biological or biologically-mediated oxidation are used. Chemical reduction is the process by which the oxidation state, the valence, of an atom is reduced. Every oxidation reaction is accompanied by a reduction reaction and these reactions are termed Redox Reactions. For inorganic Redox Reactions, oxidation and reduction are brought about by electron transfer. Oxidation is the loss of electrons and reduction is the gain of electrons by an atom. In the below example: 2 0 2 S + I 2I + S − − → (1.1) Sulphide ion is oxidised to elemental sulphur by losing two electrons, while elemental iodine is reduced to iodide ion by gaining two electrons. In the organic 2 Chemical Oxidation Applications for Industrial Wastewaters reactions, the mechanism is more complex. An organic reaction oxidation is carried out by replacement of one of the electrons making up the covalent bond between two atoms, by changing one of the atoms in a way for reversing the order of electronegativities of the atoms. If atoms A and B are tied up with a covalent bond and atom A is more electronegative than atom B, replacement of atom B by atom C which is more electronegative than atom A, through breaking the A-B bond and formation of an A-C bond, results in the oxidation of atom A.
eBook - PDFChemistry
The Molecular Nature of Matter
- James E. Brady, Neil D. Jespersen, Alison Hyslop(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Oxidation and reduction reactions (Section 5.1) In an oxidation reaction, the substance loses electrons; in a reduction reaction, the reactant gains electrons. Oxidation and reduction reactions always occur together. Ion–electron method for acidic solutions (Section 5.2) Use this method when you need to obtain a balanced net ionic equation for a redox reaction in an acidic solution. Ion–electron method for basic solutions (Section 5.2) Use this method when you need to obtain a balanced net ionic equation for a redox reaction in a basic solution. Oxidizing and nonoxidizing acids (Table 5.2, Section 5.3) Nonoxidizing acids will react with metals below hydrogen in Table 5.3 to give H 2 and the metal ion. Activity series of metals (Table 5.3, Section 5.4) A metal in the table will reduce the ion of any metal above it in the table, leading to a single replacement reaction. Combustion with oxygen (Section 5.5) Hydrocarbon combustion with plentiful supply of oxygen hydrocarbon + O 2 h CO 2 + H 2 O (plentiful supply of O 2 ) Hydrocarbon combustion with limited supply of oxygen hydrocarbon + O 2 h CO + H 2 O (limited supply of O 2 ) Hydrocarbon combustion with extremely limited supply of oxygen hydrocarbon + O 2 h C + H 2 O (very limited supply of O 2 ) Combustion of compounds containing C, H, and O Complete combustion gives CO 2 and H 2 O, (C, H, O compound) + O 2 h CO 2 + H 2 O (complete combustion) Combustion of organic compounds containing sulfur If an organic compound contains sulfur, SO 2 is formed in addition to CO 2 and H 2 O when the compound is burned. Tools for Problem Solving The following tools were introduced in this chapter. Study them carefully so that you can select the appropriate tool when needed. Review Problems 243 = WileyPLUS, an online teaching and learning solution. Note to instructors: Many of the end-of-chapter problems are available for assignment via the WileyPLUS system.
eBook - PDF- Leo J. Malone, Theodore O. Dolter(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
pp. 480−481 14-1.2 An electron exchange reaction is known as an oxidation-reduction, or simply redox, reaction. p. 481 14-1.2 The species reduced is known as the oxidizing agent; the species oxidized is known as the reducing agent. p. 481 14-1.3 Oxidation states (or oxidation numbers) are used to identify the elements that change in Redox Reactions. p. 482 14-2 The oxidation state or bridge method balances equations by focusing on the oxida- tion state changes. p. 486 14-3 The ion-electron method is used to balance half-reactions separately before adding to the total reaction. p. 489 Oxidizing and Reducing Agents reactant oxidized oxidizing agent reactant reduced reducing agent by the 88888n by the 88888n is the 8888888888n is the 8888888888n Balancing Redox Reactions in Aqueous Solution Unbalanced core reaction: X + AO - ¡XO 2- + A Acidic solution Separate into two half-reactions X ¡ XO 2 - AO - ¡ A Add H 2 O 2H 2 O + X ¡ XO 2 - AO - ¡ A + H 2 O Add H + 2H 2 O + X ¡ XO 2 - + 4H + 2H + + AO - ¡ A + H 2 O Add e - 2H 2 O + X ¡ XO 2 - + 4H + + 3e - e - + 2H + + AO - ¡ A + H 2 O Balance electron exchange 2H 2 O + X ¡ XO 2 - + 4H + + 3e - 3e - + 6H + + 3AO - ¡ 3A + 3H 2 O Add two reactions and simplify 2H + + X + 3AO - ¡XO 2 - + 3A + H 2 O To change to a basic solution Add OH - (on both sides) for each H + (2H + + 2OH - ) + X + 3AO - ¡ XO 2 - + 3A + H 2 O+ 2OH - Combine H + and OH - to make H 2 O and simplify H 2 O + X + 3AO - ¡ XO 2 - + 3A + 2OH - SUMMARY CHART EXERCISE 14-3(b) LEVEL 3: When elemental tin is placed in a nitric acid solution, a spontaneous redox reaction occurs, producing solid tin(IV) oxide and nitrogen dioxide gas. Write the equation illustrating this reaction and balance the equation by the ion-electron method. (Water is also a product.) For additional practice, work chapter problems 14-18, 14-20, 14-22, and 14-24.
eBook - PDFThermodynamics of Natural Systems
Theory and Applications in Geochemistry and Environmental Science
- Greg Anderson(Author)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
In this chapter we develop two such indexes of redox state. 11.2 Electron Transfer Reactions ............................................................................... You may not have noticed it, but we have considered two kinds of reactions in previous chapters. In some, such as ( 9.3 ), SiO 2 ( s ) + 2H 2 O = H 4 SiO 4 ( aq ) ( 9.3 ) all elements on the right side have the same number of electrons that they have on the left side – there is no change in valence of any element. In others, such as ( 9.16 ), CH 4 ( g ) + O 2 ( g ) = CO 2 ( g ) + 2 H 2 ( g ) ( 9.16 ) there is such a change. For example, the carbon in CH 4 is C 4 − , and the carbon in CO 2 is C 4 + . Each carbon atom in methane that changes to a carbon atom in carbon dioxide must 258 Redox Reactions get rid of eight electrons – it is oxidized . Where do the electrons go? Obviously, they go to the other actors in the reaction. Oxygen in O 2 has a valence of zero (O 0 ), while in carbon dioxide it is − 2 (O 2 − ), so, in changing from O 2 to CO 2 , two oxygens gain four electrons. The other four electrons go to hydrogen, which has a valence of + 1 (H + ) in methane and zero in hydrogen gas. Both oxygen and hydrogen are reduced , if the reaction goes from left to right as written. Similarly in reaction ( 9.15 ), 6 Fe 2 O 3 ( s ) = 4 Fe 3 O 4 ( s ) + O 2 ( g ) ( 9.15 ) we see that all of the iron atoms in Fe 2 O 3 are ferric iron (Fe 3 + ), while one out of three iron atoms in Fe 3 O 4 is ferrous iron (Fe 2 + ). The iron is partially reduced, while some oxygen in Fe 2 O 3 is oxidized to O 2 ( g ) – there is a transfer of electrons from iron to oxygen, or from oxygen to iron, depending on which way the reaction goes. Without such electron transfers, these and many other reactions, including many necessary to life processes, could not proceed. 11.3 The Role of Oxygen ...............................................................................
eBook - PDF- John Wrigglesworth(Author)
- 1997(Publication Date)
- CRC Press(Publisher)
5 Redox Reactions i n Metabol ism 5.1 Oxidation states exergonic reactions in metabolism involve redox reac-tions. Someti mes there is a change in the charge on a mole-cule, for example cytochrome c 2+ being oxidised to cytochrome c 3+ , but often there is no obvious alteration in electrical charge, for example the oxidation of succinate to fumarate. Chemists have introduced the usef ul concept of oxidat ion number or oxidation state of individual atoms in a molecule. This is an artificial aid or 'bookkeeping ' device to help keep track of Redox Reactions between, and even within, molecules and can be extremely useful when studying the bioenergetics of metabolism. The oxidation number of an atom is defined as the charge the atom would have if all its bonds were considered completely ionic (the bond orbitals being fully displaced towards one atom). The number is expressed relative to the free element, whic h is defined to have an oxidation number of zero. For an atom of oxygen (the free element), has an oxidation number of o. Saturating the outer valancy shell the addition of two elec-trons to make 0 2 � makes the ionic form of oxygen with an oxidation number of -2. Molecu lar oxygen, where two oxygen atoms share their valence electrons, has an oxidation number of -4. In other words, 4 electrons would have to be added to a molecule of oxygen to make each atom completely ionic. ·' 0· '0 G.. .. .. ..e + molecular oxygen (oxidation number � 4) + ' 0 '· • 0 ion ic oxygen (oxidation number -2) Hydrogen usually forms compounds with other atoms that are more electronegative. It can be of as acting as a reductant. In tha t case, its oxidation number is +1: H O -I> hydrogen atom (oxidation number 0) H + + e-hydrogen ion (oxidation number + 1) 71 7 2 E N E R G Y A N D LI F E Oxygen in water has an oxidati on number o f -2 , since we assign the pair of electrons in the covalent bond betw e en oxygen and hydrogen to the more electronegative oxygen atom.
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