Che 320 exp IV emre - 1. INTRODUCTION The relationship...

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1. INTRODUCTION The relationship among degrees of freedom, number of components in a system at equilibrium and the number of chemical species is given by the Gibbs phase rule, which can also be defined as phase rule [1]. If no reactions occur among the system components, the phase rule is; F = C – P + 2 Where F is the degrees of freedom, C is the number of components and P is the number of phases. The degree-of freedom denotes the number of process variables that must be determined for a process system before other variables can be calculated. In the Gibbs phase rule degrees of freedom equals the number of intensive variables that must be specified for a system at equilibrium before remaining intensive variables can be calculated. [1] If the phase rule is applied to the ternary systems, number of components is three. So in the Gibbs phase rule equation C becomes 3. After determining the number of components, number of phases must be determined. If the system is homogenous, then the number of phases is one, and the degrees of freedom is calculated as; F = 3 – 1 + 2 = 4 So, four variables must be determined in order to define the system. These are pressure, temperature and the mass fractions of the two components. On the other hand; if the system is two phases, then the number of phases is two, and the degrees of freedom become as; F = 3 – 2 + 2 = 3 These three variables are temperature, pressure and the composition of the one component in the system. In this experiment the system is ternary system, which means three liquid species are involved. One of which is completely miscible in the other two in all proportions where as the other two are slightly soluble in one another. In other words, acetic acid – water and acetic acid – toluene mixtures are mixed in all proportions whereas water – toluene mixture is slightly soluble. 1
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corner of the triangle shows pure components. In general, the component which is miscible in the other two, fit up at the top of the triangle. The other two species are fit up at the bottom corners randomly. The equilateral triangle consists of two main parts, which are separated by binodal curve (solubility curve). The region under the curve is the two phase region. This means if the mixture composition corresponds under the binodal curve, the mixture separates two different liquid layers. On the other hand, the mixture, which has a composition in the region above the binodal curve, is a single-phase liquid. The binodal curve is obtained from the first points at which two phase turns to a single-phase. These are represented at the Figure 1.1. Figure 1.1 : A sample solubility curve (not for making calculations) A composition of the three components mixture can be shown in the equilateral triangular coordinates as a point. For example; point A contains 60% Acetic acid, 10% Toluene and 30% Water can be shown as in Figure 1.1. 2
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This note was uploaded on 05/01/2011 for the course CHE che 320 taught by Professor Ahmetarslan during the Spring '11 term at Middle East Technical University.

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Che 320 exp IV emre - 1. INTRODUCTION The relationship...

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