Phases and Physical States of Matter

CHAPTER 2 SYSTEMS AND THEIR PROPERTIES 2.2 PHASES AND PHYSICAL STATES OF MATTER... 

The previous chapter dealt with chemical bonding and the forces present between the atoms in molecules. Forces between atoms within a molecule are termed intramolecular forces and are responsible for chemical bonding. The interaction of valence electrons between atoms creates intramolecular forces, and this interaction dictates the chemical behavior of substances. Forces also exist between the molecules themselves, and these are collectively referred to as intermolecular forces. Intermolecular forces are mainly responsible for the physical characteristics of substances. One of the most obvious physical characteristics related to intermolecular force is the phase or physical state of matter. Solid, liquid, and gas are the three common states of matter. In addition to these three, two other states of matter exist—plasma and Bose-Einstein condensate. 

In earlier chapters, we investigated the nature of the solid, liquid, and gaseous states of matter in this chapter, we extend the discussion and look at transformations between these states. The discussion introduces the concept of equilibrium between different phases of a substance, and that concept will prove to be of the greatest importance when, in the following chapter, we turn to chemical transformations. The presence of solutes alters the physical properties of the solvent and gives rise to a number of important effects, including the flow of nutrients into and out of living cells. 

Let us first discuss the phase diagram of water. The phase diagrams show the thermodynamically stable physical states of matter at different temperatures and pressures. Within each phase, the material is uniform with respect to its chemical composition and physical state. At typical temperatures and pressures on Earth (T = 298 K (25°C) andV = 1 atm) water is a liquid, but it becomes solid (that is, ice) if its temperature is lowered below 273 K (0°C) and gaseous (that is, water vapor) if its temperature is raised above 373 K (100°C), at the same pressure. Each line (phase coexistence line) on a phase diagram represents a phase boundary and gives the conditions when two phases may stably coexist (in any relative proportions) [1]. 

A phase transition is transformation of a thermod3mamic system from one phase or state of matter to another. A phase of a thermod3mamic system and the states of matter has essentially uniform physical properties. During a phase transition of a given medium, certain properties of the medium change, often discontinu-ously, as a result of some external condition, such as temperature, pressure, and others. 

A phase is a state of matter that is uniform throughout, both in chemical composition and in physical state. Thus ice, water and steam are three separate phases as are diamond, graphite and Cso-... 

Liquid crystals represent a state of matter with physical properties normally associated with both soHds and Hquids. Liquid crystals are fluid in that the molecules are free to diffuse about, endowing the substance with the flow properties of a fluid. As the molecules diffuse, however, a small degree of long-range orientational and sometimes positional order is maintained, causing the substance to be anisotropic as is typical of soflds. Therefore, Hquid crystals are anisotropic fluids and thus a fourth phase of matter. There are many Hquid crystal phases, each exhibiting different forms of orientational and positional order, but in most cases these phases are thermodynamically stable for temperature ranges between the soHd and isotropic Hquid phases. Liquid crystallinity is also referred to as mesomorphism. 

Intermolecular forces are responsible for the existence of several different phases of matter. A phase is a form of matter that is uniform throughout in both chemical composition and physical state. The phases of matter include the three common physical states, solid, liquid, and gas (or vapor), introduced in Section A. Many substances have more than one solid phase, with different arrangements of their atoms or molecules. For instance, carbon has several solid phases one is the hard, brilliantly transparent diamond we value and treasure and another is the soft, slippery, black graphite we use in common pencil lead. A condensed phase means simply a solid or liquid phase. The temperature at which a gas condenses to a liquid or a solid depends on the strength of the attractive forces between its molecules. 

As I look back at this experience, it was an awesome adventure to be alone, during and for an interval of time after this discovery, with the apparatus showing one new effect after another, when there was no one in the Illinois Physics Department experienced in NMR with whom I could talk. Little did the early NMR resonance community realize that the analogue of spin echo hidden memory contained in excited phases of all kinds of states of matter, including plasmas, would be obtained in the future by use of optical laser, electric, and acoustic pulses as well. And now today the use of spin echoes is a standard procedure for magnetic resonance imaging of the human body for medical diagnosis. 

A phase is defined as a state of matter that is uniform throughout in terms of its chemical composition and physical state in other words, a phase may be considered a pure substance or a mixture of pure substances wherein intensive properties do not vary with position. Accordingly, a gaseous mixture is a single phase, and a mixture of completely miscible liquids yields a single hquid phase in contrast, a mixture of several solids remains as a system with multiple solid phases. A phase rule therefore states that, if a limited number of macroscopic properties is known, it is possible to predict additional properties. 

A temperature-pressure graph showing the various states of matter is a phase diagram. Phase refers to a single homogeneous physical state. Different phases have either different compositions or different physical states. In the preceding figure, there are 3 phases with the same composition solid, liquid, and gas. 

Property parameters. The physical property parameters include state of matter, phase equilibrium, thermal, mechanical, optical, and electromagnetic properties. The chemical property parameters include preparation, reactivity, reactants and products, kinetics, flash point, and explosion limit. The biological property parameters include toxicity, physiological and pharmaceutical effects, nutrition value, odor, and taste. 

The approach to the critical point, from above or below, is accompanied by spectacular changes in optical, thermal, and mechanical properties. These include critical opalescence (a bright milky shimmering flash, as incident light refracts through intense density fluctuations) and infinite values of heat capacity, thermal expansion coefficient aP, isothermal compressibility /3r, and other properties. Truly, such a confused state of matter finds itself at a critical juncture as it transforms spontaneously from a uniform and isotropic form to a symmetry-broken (nonuniform and anisotropically separated) pair of distinct phases as (Tc, Pc) is approached from above. Similarly, as (Tc, Pc) is approached from below along the L + G coexistence line, the densities and other phase properties are forced to become identical, erasing what appears to be a fundamental physical distinction between liquid and gas at all lower temperatures and pressures. 

SURFACE. In physical chemistry the area of contact between two different phases or states of matter, e.g., finely divided solid particles and air or other gas (solid-gas) liquids and air (liquid-gas) insoluble particles and liquid (solid-liquid). Surfaces are the sites of tire physiochemical activity between the phases that is responsible for such phenomena as adsorption, reactivity, and catalysis, The depth of a surface is of molecular order of magnitude, The term interface is approximately synonymous with surface, but it also includes dispersions involving only one phase of matter, i.e., solid-solid or liquid-liquid,... 

Solid thin films are common study objects in most phases of solid state physics. They supply the samples for the study of general structural and physical properties of solid matter where special beam methods require small quantities of material or extremely thin layers. 

A phase is defined as any homogeneous, physically distinct part of a system which is mechanically separable and bounded by a definite surface. A phase can exist in either state of matter, viz., solid, liquid or gas. A system may consist of one phase or more than one phases. 

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