Entropy chemical equilibrium

A special case of opposing reactions is the one in which chemical equilibrium has been attained, but not isotopic equilibrium. Isotopic equilibration reactions are termed exchange reactions. They occur with virtually no net driving force i.e., AG 4 is very nearly zero, save for that provided by the entropy of isotopic mixing. 

What Are the Key Ideas Tlic direction of natural change coi responds 10 the increasing disorder of energy and matter. Disorder is measured by the thermodynamic quantity called entropy. A related quantity—the Gibbs free energy—provides a link between thermodynamics and the description of chemical equilibrium. 

Why Do We Need to Know This Material The second law of thermodynamics is the key to understanding why one chemical reaction has a natural tendency to occur bur another one does not. We apply the second law by using the very important concepts of entropy and Gibbs free energy. The third law of thermodynamics is the basis of the numerical values of these two quantities. The second and third laws jointly provide a way to predict the effects of changes in temperature and pressure on physical and chemical processes. They also lay the thermodynamic foundations for discussing chemical equilibrium, which the following chapters explore in detail. 

The estimation of the number of Frenkel defects in a crystal can proceed along lines parallel to those for Schottky defects by estimating the configurational entropy (Supplementary Material S4). This approach confirms that Frenkel defects are thermodynamically stable intrinsic defects that cannot be removed by thermal treatment. Because of this, the defect population can be treated as a chemical equilibrium. For a crystal of composition MX, the appropriate chemical equilibrium for Frenkel defects on the cation sublattice is... 

Balzhiser, R. E., Samuels, M. R. and Eliassen, J. D. Chemical Engineering Thermodynamics The Study of Energy, Entropy, and Equilibrium (Prentice-Hall, Englewood Cliffs, NJ, 1972). 

Describe how enthalpy and entropy are related to chemical equilibrium. 

In the second approach, the chemical equilibrium between the reactant(s) and the transition state is expressed in terms of conventional thermodynamic functions, i.e., enthalpy and entropy changes. This method is easier to implement and provides useful insights for estimating both the preexponential factors and the activation energies. Consequently, we shall utilize the thermodynamic formulation of the TST in this paper. 

This is a book about chemical kinetics—not necessarily the most familiar aspects of that subject, but nevertheless the various phenomena to be described arise primarily because reactions occur at finite rates, and different reactions may occur at different rates. Before proceeding along our kinetics course, however, it is worth while examining what information we can gain from thermodynamics. For most of us, the familiar aspects of thermodynamics are those dealing with systems at chemical equilibrium. Then we can use concepts such as enthalpy and entropy to place strong restrictions on the final equilibrium composition attained from a given set of initial reactant concentrations. 

With the discussion of the free-energy function G in this chapter, all of the thermodynamic functions needed for chemical equilibrium and kinetic calculations have been introduced. Chapter 8 discussed methods for estimating the internal energy E, entropy S, heat capacity Cv, and enthalpy H. These techniques are very useful when the needed information is not available from experiment. 

Thermodynamics and Equilibrium Second We present chemical equilibrium from the viewpoint of thermodynamics. We believe that the quantitative formulation of equilibrium should rest on an understanding of free energy and entropy. To this end, we introduce the laws of thermodynamics before equilibrium, and we formulate equilibrium concepts in terms of standard free energies. This approach allows us to present a unified treatment of a wide range of chemical processes. 

When a chemical reaction is proceeding, it is, by definition, not at equilibrium and thus not reversible. Thus, entropy changes in chemical reactions cannot be obtained from heat effects in calorimetric experiments. Entropy changes can be obtained by studying chemical equilibrium (Chapter 7) or by opposing the tendency of the reaction to proceed with an applied electric potential (Chapter 10). 

ISBN-10 1-4051-3997-8 (pbk. alk. paper) 1. Thermodynamics. 2. Chemical equilibrium. 3. Entropy. 4. Thermochemistry I. Title. 

The constant of integration in Eq. (1.13) cannot be determined by thermodynamics. It is of no practical importance when we are considering the gas by itself, for in all cases we have to differentiate the entropy, or take differences, in our applications. But when wc come to the equilibrium of different phases, as in the problem of vapor pressure, and to chemical equilibrium, we shall find that the constant in the entropy is of great importance. Thus it is worth while devoting a little attention to it here. There is one piece of information which we can find about it from thermo-... 

For small values of X (near chemical equilibrium state), the linear term predominates in Eq. (8.40), and the entropy production becomes... 

Exothermic reactions with a decrease in entropy reach equilibrium (AG = 0) at some temperature and reverse beyond this point. This is evident from Eq. (4.2) where the negative term AH will cancel with the positive term TAS when T gets sufficiently large. Since we already noted that such reactions are common in the chemical industry, should we expect most reactions to be reversible In principle, yes, but in practice we operate many reactors at a temperature far below the equilibrium point and therefore never notice any influence of the reverse reaction. There are, however, industrially important exceptions to this rule. The manufacture of ammonia from nitrogen and hydrogen and the formation of sulfur trioxide from sulfur dioxide and oxygen are two prominent cases. 

Thermodynamic analyses, in the form of calculations of chemical equilibrium state, have been done for many CVD systems. However, they require data on the enthalpy, entropy and heat capacity for all molecules to be considered, and such data are not always available, especially for the newer CVD precursors. Constraints can be imposed on equilibrium calculations as a way... 

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