相律 Phase rules Phase diagrams are extremely useful for systems with multiple components, and serve to describe physical and chemical equilibria over a range of different compositions, as well as points where substances are mutually miscible, or even when a system has to be brought to a specific set of conditions for equilbrium to exist(e.g, pressure, temperature and composition) Phase diagrams are very important in the development of alloys ceramic materials steels ■ semiconductors plastIcs superconductors cosmetics petroleum product separations food products glasses All phase diagrams are developed around one relationship, the phase rule, which was derived by J.W. Gibbs-it can be applied to a wide variety of systems Phase diagrams: pictorial way of understanding the properties of a system
相 律 Phase Rules
相律 Phase rules 1. fE Phase Signifies a form of matter that is uniform throughout, not only in chemical composition but also in physical state 2.相数 Phase number Number of phases is denoted by P P=1 for gas, gaseous mixture, crystal, two miscible liquids, ice P= 2 for slurry of ice and water, immiscible metal alloys Sometimes not easy to decide how many phases there are-for example, a solution of solid A in solid B- homogeneous on molecular scale-a atoms are surrounded by b atoms, representative of composition on the whole(example a) A dispersion (example b) is uniform macroscopically, but not on the microscopic molecular level -for examples, regions of a are embedded withing a matrix of B, still uniform composition-very important in materials synthesis, especially production of steels b tailoring materials mechanical and electrical properties
相 律 Phase Rules 1. 相 Phase 2. 相 数 Phase Number
相律 Phase rules 3.物种数 Constituent: A chemical species that is present in a system. For example, a mixture of water and ethanol has 2 consituents 4.组分数C Component: a chemically independent component of the system. The number of components in a system, C, is the minimum number of independent species needed to define the composition of all of the phases present in the system When no reaction takes place, Consituents= Components When a reaction can occur, the number of components is the minimum number of species which specifies the composition of all of the phases
相 律 Phase Rules 3. 物种数 4. 组分数 C
相律 Phase rules 例1 CaCO3(s)= Cao(s) Co2(g Phase 1 Phase 2 Gas phase Number of phases, P=3 Number of constituents 3 Number of Components, C=2 CacO, can be expressed in terms of 2 components in two different phases from the stoichiometry of the reaction 1jJ2 Consider the thermal decomposition of ammonium chloride NH,CI(s NH3(g) HcI (g) Number of phases P=2 Number of constituents 3 Number of Components, C=1 NH3 and HCl are fixed in stoichoimetric proportions by the reaction, and compositions of both phases can be specified by nhcl 组分数C=物种数一独立化学平衡数一独立浓度关系数 注意独立浓度关系只限于同一相中
相 律 Phase Rules 例1 例2 组分数 C = 物种数 – 独立化学平衡数 – 独立浓度关系数 注意:独立浓度关系只限于同一相中
相律 Phase rules 组分数C=物种数一独立化学平衡数一独立浓度关系数 注意独立浓度关系只限于同一相中 Fi]3 Consider the thermal decomposition of ammonium chloride NH4CI(s) NH3(g) HCl(g) N B, if additional HCl or NH3 were added to the system, decomposition of the Nhcl would not give the correct gas phase compositions, and either HCl or NH would be invoked as a 2nd component 例4 H2O() 1202(g) H2(g)(at room temp) Number of phases. P=2 Number of constituents 3 Number of Components, C= 3* At room temperature, O2(g)and H ,(g) do not react to form water they are not in equilibrium regarded as independent constituent,so
相 律 Phase Rules 例3 例4 组分数 C = 物种数 – 独立化学平衡数 – 独立浓度关系数 注意:独立浓度关系只限于同一相中