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The Standard State Gibbs Energy of Reaction
The first term on the right side of Eqns. 17.12 and 17.16, , is called the standard state Gibbs energy of reaction at the temperature of the reaction, which we will denote . The standard state Gibbs energy of reaction is analogous to the standard state heat of reaction introduced in Section 3.6. The standard state Gibbs energy for reaction can be…
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The Equilibrium Constant
We now focus on the second summation of Eqn. 17.12. The ratio appearing in the logarithm is known as the activity, (cf. Eqns. 11.23 for a liquid, but now in a general sense): activity The numerator represents a mixture property that changes with composition. We have developed methods to calculate in Eqns. 10.61 (ideal gases), 10.68 (ideal solutions), 11.14 (real solution using…
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Reaction Equilibrium Constraint
Several sub-steps are involved in the procedure outlined in Section 17.1 steps (1) and (2) to find the equilibrium constant. In this section, we derive the equilibrium constraint, and then show how the thermodynamic properties are used to simplify to Eqn. 17.1. At reaction equilibria, the total Gibbs energy is minimized. If the composition of a system is…
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Introduction
You have probably performed some reaction equilibrium computations before, usually in high school or freshman chemistry. This chapter shows how the “activities” (partial pressures for ideal gases) of products divided by reactants can be related to a quantity, Ka, that does not depend on pressure or composition, and despite its dependence on temperature, it is called…
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Homework Problems
Phase Behavior 16.1. A binary mixture obeys a simple one-term equation for excess Gibbs energy, GE = Ax1x2, where A is a function of temperature: A = 2930 + 5.02E5/T(K) J/mol. a. Does this system exhibit partial immiscibility? If so, over what temperature range? b. Suppose component 1 has a normal boiling temperature of 310 K, and component 2 has a normal boiling temperature of…
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Practice Problems
P16.1. Consider the methanol(1) + water(2) + acetone(3) system with a feed shown in Figure 16.10(a). Rate each of the following products as impossible or possible, and explain. (ANS. impossible; impossible; possible; impossible.)
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Classification of Binary Phase Behavior
Since 1970 there have been several reviews and classifications of phase behavior2,3,4,5,6,7,8,9,10,11. The types are usually summarized by the projection of their phase boundaries onto two-dimensional pressure-temperature diagrams. Type I and II phase behavior have already been discussed, and they are shown by the upper two plots in Fig. 16.3. Note that azeotropic behavior is a…
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Phase Behavior Sections of 3D Objects
Several types of phase behavior may occur in binary systems.1 In earlier chapters, we explored phase behavior by examining P-x-y or T-x-y diagrams. In this section we demonstrate how these phase diagrams are related to the three-dimensional P-T-x-y diagrams. The P-x-y and T-x-y diagrams are two-dimensional cross sections of the three-dimensional phase envelope, and by studying the phase envelope, the progressions of changing shapes of the two-dimensional…
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Homework Problems
15.1. Using Fig. 15.5 on page 602, without performing additional calculations, sketch the P-x-y diagram at 400 K showing the two-phase region. Make the sketch semi-quantitative to show the values where the phase envelope touches the axes of your diagram. Label the bubble and dew lines. Also indicate the approximate value of the maximum pressure. 15.2. Consider two gases that follow the…
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Practice Problems
P15.1. Repeat all the practice problems from Chapter 10, this time applying the Peng-Robinson equation. P15.2. Acrolein (C3H4O) + water exhibits an atmospheric (1 bar) azeotrope at 97.4 wt% acrolein and 52.4°C. For acrolein: Tc = 506 K; Pc = 51.6 bar; and ω = 0.330; MW = 56. a. Determine the value of kij for the Peng-Robinson equation that matches this bubble pressure at the same…