Chemical Engineering - Phases Change Definition

Chemical Engineering - Phases Change DefinitionIn chemical engineering, the phase change definition has been followed since its inception. While the description of the term itself is relatively new to the more complicated and accurate definitions, the process has evolved over time to include the addition of several phases as well as an increasing understanding of the interactions among the components.The original definition was that a chemical change is made between two substances when the two react and the phase separation takes place. The definition is not related to either time or temperature, but rather refers to chemical reactions which occur in a liquid, vapor, solid, or gas environment. These types of processes have been recognized in a number of ways over the years and different approaches have been chosen to describe them.The original phase change chemical definition uses two characteristics of the reaction to make its definition effective. First, the reaction must take plac e at equilibrium; second, the reaction must leave the solution unchanged (and clear of any gas, solid, or liquid that had become part of the solution). In many cases, these conditions are easy to meet in a laboratory setting, making this process relatively simple to understand. However, a number of problems can occur in laboratory settings where a wide variety of chemicals are involved, many of which will not match these two characteristics.Phase change definitions which try to find the equilibrium of the reaction must often have to analyze the general behavior of the reaction over a large range of temperatures, as well as under a wide range of pressures. All reactions take place with the same temperatures and pressures during these different conditions, and so even when the reaction occurs at equilibrium for a particular temperature and pressure, it will not be easy to measure. Additionally, because the products of a reaction change as they change with temperature and pressure, it is not always possible to specify the reactions for which these conditions have been evaluated.Other changes in the definition which have been made over the years have included descriptions that do not solely include the phase change properties. When used together, these properties are often referred to as the state transition and include the inability of the material to be completely mixed with the solvent in the new condition. The state transition property does not indicate the material's ability to be completely mixed with the solvent; instead, it indicates that the material cannot become entirely one state with the solvent. The property is useful for specifying materials which may not be completely capable of being completely mixed, or which have some additional property that prevents complete mixing.Another change has been made to the phase change definition to help describe how a product reacts with the phase during a reaction. In the early days of the compound definition, pro ducts reacted with the phase, not with the solvent. This made it difficult to determine how one compound behaved differently from another, and it also left room for quite a bit of variation among the compounds in a batch of reaction reagents.A few other changes have been made to the phase change definition in recent years to include the presence of an intermediate substance, and/or how the phases interact with each other. Some properties have been defined as chemical properties, but are defined by the component in question, and other properties have been defined to help describe the actual equilibrium state of the chemical reaction.