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Chapter

Cover Aqueous Acid-Base Equilibria and Titrations

Other ionic equilibria  

This chapter assesses other ionic equilibria. Many ionic equilibria can be described through formalisms similar to that used for acid-base phenomena. The chapter briefly illustrates this, without going into detail. The successive complexation of metal ions by ligands has many feature in common with the stepwise protonation bases. However, there is one difference: the formation of metal-ligand complexes is typically described in terms of formation constants rather than ligand dissociation constants, where the latter would be the direct analogues of acid dissociation constants. The chapter then looks at the process of extraction, in which a given species is distributed over two contacting fluid phases. The extraction of metal ions often exploits their complexation equilibria, especially the much greater solubility in a non-polar organic phase of neutral over charged complexes. The chapter also considers solubility problems, precipitation titrations, and redox equilibria.

Chapter

Cover Thermodynamics of Chemical Processes

Why thermodynamics?  

This chapter provides a background on predicting and understanding the behaviour of substances, chemical reactions, and processes. It explains thermodynamics as a study that is concerned with macroscopic systems, emphasizing large, measurable amounts of matter rather than individual molecules. It also analyses the chemical context of the name thermodynamics, which is considered a misnomer as it is useful in fundamental studies of understanding what drives chemical reactions and processes. The chapter focuses on chemical reactions and phase equilibria as the two main areas to which chemical thermodynamics can be applied. It cites the combustion of methane as an example of a reaction that goes to completion, as no methane is left after combustion if there is enough oxygen available.

Chapter

Cover Atkins’ Physical Chemistry

Adsorption and desorption  

This chapter looks at the extent to which molecules attach themselves to a surface, which is crucial to understanding the way in which a surface influences chemical processes. It discusses the extent of adsorption that can be explored with the aid of some simple models that allow quantitative predictions to be made about how the extent of surface coverage varies with both pressure and temperature. It also demonstrates how surfaces can affect the rates of chemical reactions by assessing the extent of surface coverage and the factors that determine the rates at which molecules attach to and detach from solid surfaces. The chapter outlines the extent of surface coverage that can be expressed in terms of isotherms derived on the basis of dynamic equilibria between adsorbed and free molecules.

Chapter

Cover Foundations of Organic Chemistry: Worked Examples

Mechanisms  

This chapter outlines the classification of reactions, reagents, and bond-making/breaking and covers substitution, addition, elimination, nucleophilic, electrophilic, radical, homolytic, and heterolytic. It reviews mechanisms that use curly arrows, energy profiles, intermediates, transition states, equilibria, and kinetics. It also describes the nucleophile which include four nonbonded pairs of electrons and donate an electron pair to make a new bond. The chapter discusses electrophiles that can accept a pair of electrons, radicals that has an unpaired electron, and polarized molecules. It mentions how the loss of one electron from a bromine atom brings aboutthe six-electron, positively charged Br+ ion.

Chapter

Cover Modern Liquid Phase Kinetics

Introduction  

This chapter introduces two separate objects of chemical kinetics, which are the analysis of the mechanism by which a reaction occurs, and the determination of the absolute rate of the reaction or its individual steps. It explains that kinetics is concerned with the passage towards equilibrium, particularly with the details of the process whereby a system moves from one state to another, and with the time required for the transition. It also describes the routes to equilibrium, of which there are many. The rates of chemical transformations constitute a more intricate problem than equilibria. The chapter analyses chemical primary processes which include a transition between two atomic or molecular states separated by a potential barrier. It also mentions the time-range over processes of a variety of chemical compounds and reactions which occur in more than twelve orders of magnitude.

Book

Cover Foundations of Physical Chemistry: Worked Examples

Nathan Lawrence, Jay Wadhawan, and Richard Compton

Foundations of Physical Chemistry presents a grounding in the field of physical chemistry. The early chapters cover the structure of atoms, ions and molecules, reactivity, kinetics, and equilibria. The final chapter gives an insight into more advanced areas, drawing on real-world examples.

Chapter

Cover Foundations of Physical Chemistry: Worked Examples

Chemical equilibria  

This chapter gives a range of problems that explain the Le Chatelier's principle and equilibrium constants and chemical speciation in both gases and solutions. It describes the relationship between the standard Gibbs free energy changes of a reaction and the equilibrium constant for the reaction. It also covers acid-based equilibria, complex-ion formation, solubility of solids, and redox equilibria. The chapter shows the phase diagrams of water and carbon dioxide and provides a comment on the variation of the phase boundaries with temperature and pressure. It reviews the trends influencing the pressure-temperature behaviour of the melting point, such as the endothermic nature of the melting process wherein the higher temperature encourages the formation of the liquid phase.

Chapter

Cover Nuclear Magnetic Resonance

Chemical exchange  

P.J Hore

This chapter evaluates the theory of chemical exchange, which is straightforward compared to the complex computations required to obtain chemical shifts and J-couplings. Chemical exchange effects in nuclear magnetic resonance (NMR) arise from dynamic chemical and conformational equilibria. The chapter studies the cases of symmetrical two-site exchange and unsymmetrical two-site exchange. NMR lines are broadened by slow exchange. Meanwhile, differences in the NMR frequencies of exchanging spins (δν) can be averaged by fast exchange. The magnitude of δν relative to the exchange rate constant(s) determines whether the exchange is 'slow' or 'fast'. Ultimately, chemical exchange effects give information on the rates and mechanisms of chemical reactions, molecular rearrangements, and internal motions.

Chapter

Cover Process Development

Equilibria in multiphase systems  

This chapter addresses equilibria in multiphase systems. Many processes are operated under conditions where more than one phase is present. This is often due to economic considerations: when it is necessary to contact large water-insoluble reactants with inorganic reagents, reactions are frequently run with either a separate solid phase or else a solution phase containing the inorganic reagent. Workup processes frequently involve the washing of a solution of a water-insoluble product which is dissolved in an organic solvent such as toluene with water in order to remove inorganic residues. The chapter then looks at simple distribution equilibria; solubilities of ionisable substrates; liquid–liquid partition of ionisable substrates; and ternary phase diagrams.

Chapter

Cover Making the Transition to University Chemistry

Chemical Equilibrium  

This chapter introduces equilibria and equilibrium constants. Equilibrium is recorded when the rate of the forward reaction equates to the rate of the backwards reaction. When equilibrium has been reached, the concentrations of all the substances remain constant. The thermodynamic equilibrium constant is devised when the standard Gibbs energy change is in line with the natural logarithm of the equilibrium constant. The chapter lists the equilibrium calculations mostly used in universities. Le Chatelier's principle refers to the small conditions changes subjected at a system in equilibrium as the equilibrium tends to shift to minimize the effect of the change.

Book

Cover Thermodynamics of Chemical Processes
Thermodynamics of Chemical Processes describes the basic principles which govern reactivity and phase equilibria in chemical systems and contains a number of worked examples and problems. The first chapter considers preamble energy in chemical systems. The second chapter covers enthalpy and thermochemistry. The next chapter is about entropy in chemistry. There follows a chapter on free energy and equilibrium. The last chapter is about phase changes and solutions.

Chapter

Cover Elements of Physical Chemistry

Proton transfer equilibria  

This chapter describes proton transfer equilibria. It begins by looking at the Brønsted–Lowry theory of acids and bases, according to which an acid is a proton donor and a base is a proton acceptor. The strength of an acid is reported in terms of its acidity constant and that of a base in terms of its basicity constant. The chapter then considers protonation and deprotonation. It differentiates between a weak acid and a strong acid. A strong acid is commonly regarded as being completely deprotonated in aqueous solution. The chapter also differentiates between a strong base and a weak base.

Chapter

Cover Physical Chemistry for the Life Sciences

The response of equilibria to the conditions  

This chapter examines the response of equilibria to various conditions. It introduces Le Chatelier's principle: ‘When a system at equilibrium is subjected to a disturbance, the composition of the system tends to adjust so as to minimize the effect of the disturbance’. The chapter shows that by exploring how the standard reaction Gibbs energy depends on the conditions, we can infer how the equilibrium constant responds. One influence that can be dismissed at the outset is the role of catalysts, which in a biochemical context means the role of enzymes. The chapter pays particular attention to the effects of pressure and temperature. It reveals that when a gas-phase reaction at equilibrium is compressed, the composition tends to adjust so as to reduce the number of molecules in the gas phase. Additionally, the chapter shows how changes in temperature, such as those brought about by certain infections, affect biological processes.

Chapter

Cover Exploring proteins: a student’s guide to experimental skills and methods

Calculations in the molecular biosciences  

This chapter addresses the analysis of some important types of biological processes. It begins by looking at the energetics of processes. In biological systems we deal with two main types of processes, namely chemical reactions in which covalent bonds are broken and made, so that one or more new compounds are made from the starting compounds, and complex formation in which two (or more) compounds can associate reversibly with one another. The science of thermodynamics is concerned with the overall changes in energy when processes occur; it can be used to predict how far a process will proceed, i.e. does the equilibrium lie more towards the side of the products or the reactants? The chapter then discusses binding equilibria; this includes the kinetics of enzyme-catalysed reactions since many of the equations involved are similar. The chapter also considers radioactivity, which is widely used to track specific compounds.

Chapter

Cover Core Maths for the Biosciences

Extension: dynamical systems  

This chapter focuses on dynamical systems, wherein the simplest nonlinear mathematical models could give rise to incredibly complex behaviour. It mentions scientists studying biological and physical processes of nature that were in the forefront of the revolution in mathematics for discovering dynamical systems. It also introduces some basic concepts of complexity theory: equilibria and stability, bifurcations, and chaos. The chapter begins with a brief snapshot of the birth of chaos theory, particularly theories of pattern formation and ecological implications. It cites the truncation error, which is another source of error in numerical methods that happens by approximating the true function by a Taylor series that is truncated after the first two or three terms.

Chapter

Cover The Physicochemical Basis of Pharmaceuticals

Pharmaceutical Equilibria  

This chapter examines pharmaceutical equilibria. Medicines are systems of several components and phases existing at equilibrium. Equilibrium processes are controlled by the energetics, or thermodynamics, of the system. Energetics and equilibrium processes control the movement of the drug molecule between phases during its transport to the target receptor. Systems then undergo change so as to minimize enthalpy and/or maximize entropy. The thermodynamic property that takes into account both the enthalpy and entropy of the system is the free energy. Many important pharmaceutical systems have many phases in which components are transferring between phases. The chapter then looks at the phase rule. During transport of a drug from the point of delivery to the target receptor, the drug molecule has to undergo a number of phase transitions. This involves mass-transfer processes, including diffusion, dissolution, partitioning, and gas absorption.

Chapter

Cover Elements of Physical Chemistry

Solubility equilibria  

This chapter highlights solubility equilibria. A solid dissolves in a solvent until the solution and the solid solute are in equilibrium. At this stage, the solution is said to be saturated, and its molar concentration is the molar solubility of the solid. That the two phases—the solid solute and the solution—are in dynamic equilibrium implies that equilibrium concepts can be used to discuss the composition of the saturated solution. A solubility equilibrium is an example of a heterogeneous equilibrium in which the species are in different phases (the solid solute and the solution). The chapter then looks at the solubility constant before considering the common-ion effect. The common-ion effect is the reduction in solubility of a sparingly soluble salt by the presence of a common ion. The chapter also examines the effect of added salts on solubility.

Chapter

Cover Foundations of Organic Chemistry: Worked Examples

Acids and bases  

This chapter discusses equilibria and factors effecting acidity and basicity of organic compounds and other areas of chemistry, such as electronegativity of the atom that bear the charge. It examines delocalization, resonance, inductive effects, indicators, and interactions between molecules and ions. It also deals with the protonation on the carbonyl oxygen atom that gives the more stable, delocalized protonated form of the COOH group. The chapter mentions the inductive electron-withdrawing effect of the C=O that helps to weaken the adjacent O-H bond and carboxylic acids that are more acidic than alcohols, whose anions are not stabilized by delocalisation. It refers to Tenormin, which is a drug used in the treatment of high blood pressure, angina, and abnormal heart rhythms.

Chapter

Cover Chemistry for the Biosciences

Equilibria: how far do reactions go?  

This chapter focuses on equilibrium reactions, which can proceed in both forward and reverse directions simultaneously. At equilibrium, the rates of the forward and back reactions are equal: they continue to proceed, but there is no overall change in the system—this is called dynamic equilibrium. The relative position of an equilibrium reaction when equilibrium has been reached is represented by an equilibrium constant. The chapter explains the reaction quotient, before looking at binding reactions and how they represent a type of equilibrium reaction. When an equilibrium is perturbed, the system acts to counteract the change so that a state of equilibrium is re-established. There are three key ways to perturb an equilibrium: by changing the concentration of species present, changing the temperature, or changing the pressure. Finally, the chapter considers the impact of free energy on chemical equilibria.

Book

Cover Process Development

John H. Atherton and Keith J. Carpenter

Process Development starts off by looking at the scope of process development and strategies for process development, before moving onto pre-reaction equilibria. There are chapters on competing reactions in homogeneous media and mixing effects in pseudo-homogeneous systems. Next, the text covers equilibria in multiphase systems. It also explains dispersion and mass transfer in multiphase systems and mass-transfer and reaction in two-phase systems. Finally, the text looks at product isolation and workup and scale-up.