tailieunhanh - Multimedia Environmental Models - Chapter 5

Bản chất của hiện tượng phân vùng Có hai nhiệm vụ riêng biệt mà phải được giải quyết khi dự đoán phân vùng cân bằng các hóa chất trong môi trường. Đầu tiên, chúng ta phải hiểu đầy đủ hóa chất hoạt động trong điều kiện phòng thí nghiệm lý tưởng, kiểm soát nhiệt độ và cũng được xác định, giai đoạn tinh khiết. Đây là nhiệm vụ của hóa học vật lý. Thứ hai là bản dịch của những dữ liệu phân vùng vào các điều kiện phức tạp hơn và ít rõ ràng hơn của môi trường nơi các. | McKay Donald. Phase Equilibrium Multimedia Environmental Models Edited by Donald McKay Boca Raton CRC Press LLC 2001 CHAPTER 5 Phase Equilibrium INTRODUCTION The Nature of Partitioning Phenomena There are two distinct tasks that must be addressed when predicting equilibrium partitioning of chemicals in the environment. First we must fully understand how chemicals behave under ideal laboratory conditions of controlled temperature and well defined pure phases. This is the task of physical chemistry. Second is the translation of these partitioning data into the more complex and less defined conditions of the environment where phases vary in composition and properties. In both cases we are concerned with the equilibrium distribution of a chemical between phases as illustrated in the simple two-compartment system of Figure . A small volume of nonaqueous phase . a particle of organic or mineral matter a fish or an air bubble is introduced into water that contains a dissolved chemical such as benzene. There is a tendency for some of the benzene to migrate into this new phase and establish a concentration that is some multiple of that in the water. In the case of organic particles the multiple may be 100 or if the phase is air the multiple may be only . Equilibrium becomes established in hours or days between the benzene dissolved in the water and the benzene in or on the nonaqueous phase. Analytical measurements may give the total or average concentration that includes the nonaqueous phase and may differ considerably from the actual dissolved water concentration. The phase may subsequently settle to the lake bottom or rise to the surface conveying benzene with it. Clearly it is essential to establish the capability of calculating these concentrations and thus the fractions of the total amount of benzene that remain in the water and enter the second phase. In some cases 95 of the benzene may migrate into the phase and in others only 5 . These systems .