Chemistry
Decomposition Reaction
A decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more simpler substances. This reaction is usually initiated by heat, light, or electricity and is the opposite of a synthesis reaction. The products of a decomposition reaction can be elements, compounds, or a mixture of both.
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eBook - ePub- Michel Soustelle(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
Chapter 13Decomposition Reactions of Solids
A Decomposition Reaction of a solid is a reaction that starting from a solid A leads to another solid B , with the release of one or more gas. Such a reaction is written as:These reactions are characterized by the change of an unstable initial solid phase under the experimental conditions into another stable final solid phase. The two solids A and B are different in their compositions and crystal structures.These reactions generally occur under the effect of temperature, given pressure conditions of gases, and sometimes the effect of electromagnetic radiations with suitable wavelengths.The majority of these reactions are possible in both directions (the opposite reaction of a decomposition is a gas-solid reaction; see Chapter 15 ) according to the conditions of temperature and pressures given by thermodynamics. The studies of the reactions in the direction of the decomposition are generally carried out under conditions that are not very far from equilibrium conditions in order to obtain suitable speeds (not too fast) for measurement; then, we will not be able to neglect the opposite reactions of the elementary steps. Including the creation of a new solid phase, Decomposition Reactions use the two processes of nucleation, in general on the surface, and growth, according to the methods developed in Chapters 10 and 11 .13.1. Classifications of Decomposition Reactions
Two kinds of classifications have been proposed for these reactions: one is based on the sign of the enthalpy of the reaction and the other on the origin of the released gas molecule.13.1.1. Classification according to the sign of the enthalpy
Some authors proposed to classify the Decomposition Reactions into two categories: exothermic reactions and endothermic reactions. This distinction is important for the experimental approach because concerned solids generally have poor heat conduction; then, the exothermic reactions can lead to over-temperatures (heating of the sample due to the heat released and difficult to evacuate it) and the endothermic reactions can lead to the opposite phenomenon of sub-temperature. These phenomena must be, either eliminated as far as possible, or taken into account in the modeling of the kinetics.
eBook - PDFChemistry for Today
General, Organic, and Biochemistry
- Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
IO 2 3 saqd 1 3HSO 2 3 saqd S I 2 saqd 1 3HSO 2 4 saqd 5.4 Decomposition Reactions Learning Objective 3 Classify reactions into the categories of redox or nonredox, then into the categories of decomposition, combination, single replacement, or double replacement. In Decomposition Reactions, a single substance is broken down to form two or more simpler substances, as shown in Figure 5.6. In this and other “box” representations of reactions, the number of molecules in the boxes will not match the coefficients of the reaction equation. However, they will be in the correct proportions. In Figure 5.6, for example, the box on the left contains the same number of H 2 O 2 molecules as the num- ber of H 2 O molecules on the right. Also, the number of H 2 O molecules on the right is twice the number of O 2 molecules. The general form of the equation for a decomposi- tion reaction is A S B 1 C (5.13) Some Decomposition Reactions are also redox reactions, whereas others are not. Examples of Decomposition Reactions are given by Equations 5.14 and 5.15: 2HgO(s) ¡ 2Hg(/) 1 O 2 (g) (5.14) CaCO 3 (s) ¡ CaO(s) 1 CO 2 (g) (5.15) Equation 5.14 represents the redox reaction that takes place when mercury(II) oxide (HgO) is heated. Mercury metal (Hg) and oxygen gas (O 2 ) are the products. This reaction was used by Joseph Priestley in 1774 when he discovered oxygen. Equation 5.15 represents a nonredox reaction used commercially to produce lime (CaO) by heating limestone (CaCO 3 ) to a high temperature. The decomposition of H 2 O 2 represented by Figure 5.3 is shown in Figure 5.7. Decomposition Reaction A chemical reaction in which a single substance reacts to form two or more simpler substances. 2H 2 O 2 2H 2 O 1 O 2 FIGURE 5.6 A Decomposition Reaction. heat heat Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Chapter 8 Chemical Reaction A thermite reaction using ferric oxide A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reactions. ___________________WORLD TECHNOLOGIES____________________ The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions. Different chemical reactions are used in combination in chemical synthesis in order to obtain a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions impossible under ordinary conditions are performed within a cell. History Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen Chemical reactions such as combustion in the fire, fermentation and the reduction of ores to metals were known since antiquity.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Research World(Publisher)
Chapter 10 Chemical Reaction A thermite reaction using ferric oxide A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass changes that strictly __________________WORLD TECHNOLOGIES___________________ involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reactions. The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically present the starting materials, end products, and sometimes intermediate products and reaction conditions. Different chemical reactions are used in combination in chemical synthesis in order to obtain a desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by which syntheses and decompositions impossible under ordinary conditions are performed within a cell. History Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen Chemical reactions such as combustion in the fire, fermentation and the reduction of ores to metals were known since antiquity.
eBook - PDF- Luca Palmeri, Alberto Barausse, Sven Erik Jorgensen(Authors)
- 2013(Publication Date)
- CRC Press(Publisher)
131 © 2008 Taylor & Francis Group, LLC 9 Chemical Reactions 9.1 Introduction The term chemical process is used to indicate a sequence of one or more operations achieving the transformation of chemicals. Chemical processes fall into three broad categories: processes performed in a chemical laboratory, industrial chemical processes carried out on an industrial scale, and natural chemical processes. Natural chemical processes are carried out in nature ide-ally without human action. These include, for example, the chemical processes that occur naturally in living organisms (including metabolism and photosyn-thesis) and the reactions of biodegradation. Chemical laboratory and industrial processes refer to chemical processes developed and engineered by man. Generally, a chemical reaction is a transformation of matter that occurs with-out measurable changes in mass, in which one or more initial chemical ele-ments change their structure and composition to create new products through the formation or breaking of chemical bonds involving an atom’s outer elec-trons. The chemical compounds present at the beginning of the reaction are called reagents or reactants ; whereas those obtained at the end of the reaction are called the reaction products . The phenomenon taking place during a chemi-cal reaction can be represented by a chemical equation.
eBook - PDFThermal Decomposition of Ionic Solids
Chemical Properties and Reactivities of Ionic Crystalline Phases
- A.K. Galwey, M.E. Brown(Authors)
- 1999(Publication Date)
- Elsevier Science(Publisher)
For example, the melting of a molecular crystal involves only redistribution of van der Waals forces and thus is not regarded as a decomposition. In contrast, the breakdown of the permanganate ion in KMnO4 is definitely a decomposition. Arrows indicate whether the parameter mentioned 50 increases ( T ) or decreases ( l ), while ($) means that changes may involve either increases or decreases. 2.5. THERMODYNAMIC FEASIBILITY OF DECOMPOSITION The simplest decompositions can be represented as: A(s) ~ B(s) + C(g) (2.5) Many reactions of this type are assumed to take place in a single stage, with no side reactions, other than the possible occurrence of the reverse process (see below). Three well-studied examples are: CaC03(s ) --~ CaO(s) + C02(g ) 4MnO2(s) ~ 2Mn203(s ) + O2(g) CuSO4.5H20(s) ~ CuSO4.3H20(s) + 2H20(g) Decompositions are frequently studied isothermally and under constant pressure. The sign of the change in Gibbs energy, AG, for the reaction will thus determine the spontaneity of the decomposition for the temperature and pressure conditions applying. From the general relationship AG = AH- T AS for the decomposition, the entropy change, AS, will almost inevitably be positive, so that the sign of AG will be determined largely by the sign of the enthalpy change, AH. If the values of AS and AH are assumed not to vary markedly with temperature, exothermic decompositions will be thermodynamically feasible at all temperatures (and hence are irreversible) and will be limited only by kinetic factors (see Chapter 3). Endothermic decompositions will only be thermodynamically feasible at temperatures greater than T= AH/AS. Below this temperature the reverse reaction, i.e. recombination, is expected. After an initial particle of the solid product phase B has appeared, the activities of both the solid reactant, A, and the solid product, B, are assumed to remain unaltered throughout the course of the decomposition (until no A remains).
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