Exploring Chemical Equilibrium

Reversible chemical reactions reach an equilibrium in which the concentrations of all reactants and products are constant. The relationship between the reactant and product concentrations is defined by the equilibrium constant, In this experiment, you will investigate the reaction in which colorless Fe + and SCN ions combine to form red FeSCN + ions. The intensity of the red color increases with the concentration of FeSCN +. The net ionic equation for this reversible reaction is Fe +(aq) + SCN (aq) FeSCN +(aq). 

Can you calculate the equilibrium constant for a chemical reaction by measuring the concentration of the reaction product  

200M Fe(N03)3 0.6M HNO3 2.00 X 10 3/w kSCN 24-well mi crop I ate thin-stern pipettes (6) sheet of white paper 

Always wear safety goggles, gloves, and a lab apron. 

Contrast homogenous and heterogeneous equilih-ria. Which type of equilibrium is represented by the reaction between Fe and SCN  

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In this chapter, we consider dynamic equilibria in chemical reactions. Chemical equilibrium occurs when opposing reactions proceed at equal rates The rate at which the products form from the reactants equals the rate at which the reactants form from the products. As a result, concentrations cease to change, making the reaction appear to be stopped. In this and the next two chapters, we will explore chemical equilibrium in some detail. Later, in Chapter 19, we will learn how to relate chemical equiHbria to thermodynamics. Here, we learn how to express the equilibrium state of a reaction in quantitative terms and study the factors that determine the relative concentrations of reactants and products in equilibrium mixtures. 

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. 

Use the Chemical Equilibrium activity (eChapter 13.1) to explore the reaction between the iron(III) ion and the thiocyanate ion. 

To explore the important characteristics of chemical equilibrium, we will consider the synthesis of ammonia from elemental nitrogen and hydrogen ... 

The concentration-based equilibrium constant embodied in Equation 9-7 on page 234 provides only an approximation to real laboratory measurements. In this chapter, we show how the approximate form of the equilibrium constant often leads to significant error. We explore the difference between the activity of a solute and its concentration, calculate activity coefficients, and use them to modify the approximate expression to compute species concentrations that more closely match real laboratory systems at chemical equilibrium. 

Recently, the phase behaviors of some reaction mixtures have been studied. To explore the advantages of the reactions under supercritical condition or in the critical region, the critical parameters and phase behavior of the reaction mixtures should be considered, and reaction properties and the phase behavior of the reaction systems should be combined in tlie study.In this section, we discuss some work about how pressure and composition of a complex reaction system affect the chemical equilibrium, conversion and selectivity and reaction rate in different phase regions. 

This chapter introduces a model for visualizing the changes that take place in a reaction mixture as a chemical reaction proceeds. The model describes the requirements that must be met before a reaction can occur, and explains why certain factors speed the reaction up or slow it down. It will help us understand why some chemical reactions are significantly reversible and why such reactions reach a dynamic equilibrium with equal rates of change in both directions. It will also allow us to explore the factors that can push a chemical equilibrium forward to create more desired products or backwards to minimize the formation of unwanted products. 

King used switching circuit theory to explore the dynamics of motion around the point in concentration space that corresponds (or would correspond) to chemical equilibrium for each of the patterns in Figure 3. Each concentration is considered to have (only) two possible conditions, high (1) or low (0). On this basis, there are eight possible overall states of the three-reagent system. Those states can be represented... 

The munber of theoretical and reactive stages is determined from the distillation line and from the intersection of the distillation line and chemical equilibrium manifold (GEM) and represents the boimdary of the forward and backward reactions) (Giessler et al., 1999). Since there are multiple pairs of X and product composition that satisfy the mass balance, the method sets one of the product composition as reference point and solves for the other two (for a 3-component system) by using material balance expressions. Thus, two of the components compositions and X lie on the same line of mass balance (LMB) in the diagram and allow the estimation of the ratio D/B at a certain reboil ratio only by exploring the ratio of the line segments (figure 3.1f>). 

The study of chanical equilibrium, explored in Chapters 10-13, can determine whether a particular reaction is possible under the given conditions and how far that reaction will proceed before equihbrium is reached. However, the laws of chemical thermodynamics and the principles of chemical equilibrium cannot determine how fast a reaction will proceed. The speed of a chemical reaction is obtained through the study of chemical kinetics, which is the area of chemistry concerned with the rates at which chemical reactions occur. The word kinetic suggests movement or change recall from Chapter 5 that kinetic energy is the energy available because of the motion of an object. Here kinetics refers to the reaction rate, which is the change in the concentration of a reactant or a product with time (M... 

In Chapter 15 we saw that equilibrium depends on Ihe rates of the forward and reverse reactions Equilibrium is reached when the opposing reactions occur at equal rates. (Section 15.1) Because reaction rates are closely tied to energy, it is logical that equilibrium should also depends in some way on energy. In this chapter we will see how chemical equilibrium is related to the energies of the reactants and products. To do so, we will take a deeper look at chanical thermodynamics, Ihe area of chemistry that explores energy relationships. 

Derivation of chemical equilibrium relationships for simple reactions Reactions in gas phase Reactions in liquid phase Explore yourself References Bibliography... 

This chapter was devoted to introducing the thermodynamic concepts and formalism essential to understand chemical reactions. Thus, we reviewed the first and second laws of thermodynamics, introduced the concept of thermodynamic equilibrium, defined the free energy change, and used it to prove that thermodynamic and chemical equilibrium are equivalent concepts. Interestingly, we were able to obtain the las of mass action Ifom purely thermodynamic considerations, suggesting that the thermodynamic and the chemical kinetics approaches are closely related. This connection is explored in detail in the next chapter. Finally, the last section of the chapter was dedicated to understanding the concept of chemical potential from the perspective of statistical mechanics. In later chapters we tackle this same question from different angles. 

A system is at chemical equilibrium when it has adjusted its chemical compositions so that the overall Gibbs energy of the system is the minimum possible, subject to the external constraints (T, P, initial chemical composition, etc.). The shorthand way of showing this is the law of mass action or chemical equilibrium constant. The relation between the two is explored in Chapter 12. 

Fully revised and expanded, this new edition deeply explores physical and chemical equilibrium, including a new appendix on the Bridgman Table and its uses, a new chapter on Equilibrium in Biochemical Reactions, and new sections on minimum work, eutectics and hydrates, adsorption, buffers and the charge-balance method of computing them. Its appendix on Calculation of Fugacities from Pressure-explicit EOSs shows clearly how modern computer equilibrium programs actually do their work using the SRK and related equations. 

Perdue EM, Lytle CR (1986) Chemical equilibrium modeling of metal complexation by humic substances. In Carlisle D, Berry WL, Kaplan IR, Watterson JR (eds) Minerals exploration biological systems and organic matter. Prentice-Hall, Englewood Cliffs, pp 428-444... 

In the next three chapters we will explore various aspects of the ideal quaternary chemical system introduced in Chapter 1. This system has four components two reactants and two products. The effects of a number of kinetic, vapor-liquid equilibrium, and design parameters on steady-state design are explored in Chapter 2. Detailed economic comparisons of reactive distillation with conventional multiunit processes over a range of chemical equilibrium constants and relative volatilities are covered in Chapter 3. An economic comparison of neat versus excess-reactant reactive distillation designs is discussed in Chapter 4. 

In this section the value of the chemical equilibrium constant at 366 K [(ATeq)366] is changed to explore its effect on the steady-state design of the reactive column. The... 

In the previous section, the optimum economic steady-state designs of reactive distillation columns were quantitatively compared with conventional multiunit systems for a wide range of chemical equilibrium constants. Relative volatilities (a = 2) were assumed constant. Reactive distillation was shown to be much less expensive than the conventional process. In this section we explore how temperature-dependent relative volatilities affect the designs of these two systems. 

Two different relative volatility rankings for a ternary decomposition reaction were explored in this chapter. The behavior of systems with an intermediate-boiling reactant is similar to the quaternary system with intermediate-boiling reactants. Systems with heavy reactant are quite different. Two possible flowsheets (two-column and one-column configurations) were discussed. The two-column flowsheet is workable for all positive chemical equilibrium constants. The one-column configuration is feasible for systems with higher chemical equilibrium constants. Economical comparisons of these two flowsheets were also given. 

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