华东理工大学：《物理化学》课程教学课件（讲稿，英文版）08 Chapter 8 Phase diagrams.pdf_大学文库

版权所有：华东理工大学物理化学教研室 2 In Chapter 6, we discussed the phase diagrams for pure substances. We shall develop their use systematically and show how they are rich summaries of empirical information about a wide range of systems. To set the stage, we introduce the famous phase rule of Gibbs, which shows the extent to which various parameters can be varied yet the equilibrium between phases preserved. With the rule established, we see how it can be used to discuss the phase diagrams that we met in the two preceding chapters. 8. Phase diagrams

版权所有：华东理工大学物理化学教研室 3 Phases, components, and degrees of freedom 8.1 Definitions 8.2 The phase rule Two-component systems 8.3 Vapour pressure diagrams 8.4 Temperature-composition diagrams 8.5 Liquid-liquid phase diagrams 8.6 Liquid-solid phase diagrams 8.7 Ultrapurity and controlled impurity 8. Phase diagrams

版权所有：华东理工大学物理化学教研室 4 8.1 Definitions 1). The phase A phase of a substance is a form of matter that is uniform throughout in chemical composition and physical state. (b) a dispersion, in which regions of one component are embedded in a matrix of a second component. (a) a single-phase solution, in which the composition is uniform on a microscopic scale

版权所有：华东理工大学物理化学教研室 5 8.1 Definitions 1). The phase The number of phases in a system is denoted P. Ice is a single phase even though it might be chipped into small fragments. A crystal is a single phase. Two totally miscible liquids form a single phase. A gas, or a gaseous mixture, is a single phase. P = 1 Any sample cut from the sample, however small, is representative of the composition of the whole

版权所有：华东理工大学物理化学教研室 6 8.1 Definitions 1). The phase An alloy of two metals is a two-phase system if the metals are immiscible. A slurry of ice and water is a two-phase system. P = 2 A dispersion of clays in water is uniform on a macroscopic scale but not on a microscopic scale. A small sample comes entirely from one of the minute grains of pure A and would not be representative of the whole

版权所有：华东理工大学物理化学教研室 7 8.1 Definitions 2). Components A constituent is a chemical species that is present in a system . A component is a chemically independent constituent of a system. The number of components, C, in a system is the minimum number of independent species necessary to define the composition of all the phases present in the system

版权所有：华东理工大学物理化学教研室 8 8.1 Definitions 2). The number of components, C No chemical reactions The pure water is a one-component system, C = 1, because we need only the species H2O to specify its composition. Similarly, a mixture of ethanol and water is a two-component system, C = 2: we need the species H2O and C2H5OH to specify its composition. When no reaction takes place, the number of components is equal to the number of constituents

版权所有：华东理工大学物理化学教研室 9 8.1 Definitions • With chemical reactions When a reaction can occur in the system, we need to decide the minimum number of species that can be used to specify the composition of all the phases. In general: C = K-R where K is the number of constituents and R is the number of independent reactions

版权所有：华东理工大学物理化学教研室 10 Example Method: there are three phases in the system. To specify the composition of the gas phase 3 we need the species CO2; and to specify the composition of phase 2 we need the species CaO. However, we do not need an additional species to specify the composition of the phase 1 because its identity (CaCO3) can be expressed in terms of the other two constituents by making use of the stoichiometry of the reaction. At the equilibrium 3 ↔ CaO(s) (s)CaCO + 2 (g)CO Phase 1 Phase 2 Phase 3 Calculate The number of components, C