Matter physical changes

Although chemists deal primarily with the chemical changes of matter, physical changes are also very important. In this section we will consider how the entropy of a substance depends on its temperature and on its physical state. 

Surfaces are found to exliibit properties that are different from those of the bulk material. In the bulk, each atom is bonded to other atoms m all tliree dimensions. In fact, it is this infinite periodicity in tliree dimensions that gives rise to the power of condensed matter physics. At a surface, however, the tliree-dimensional periodicity is broken. This causes the surface atoms to respond to this change in their local enviromnent by adjusting tiieir geometric and electronic structures. The physics and chemistry of clean surfaces is discussed in section Al.7.2. 

The thermodynamic standard state of a substance is its most stable state under standard pressure (1 atm) and at some specific temperature (usually 25°C). Thermodynamic refers to the observation, measurement and prediction of energy changes that accompany physical changes or chemical reaction. Standard refers to the set conditions of 1 atm pressure and 25°C. The state of a substance is its phase gas, liquid or solid. Substance is any kind of matter all specimens of which have the same chemical composition and physical properties. 

Another way to conceptualize drug problems is to examine psychological versus physical dependence on a substance. Psychological dependence is defined by beliefs A person thinks he or she needs the substance in order to cope. Physical dependence, on the other hand, is defined by actual physical changes related to drug use that may result in withdrawal symptoms and tolerance. However, to confuse matters, recreational users also may experience tolerance and withdrawal, so it is important to be careful when using these distinctions to define whether a person has a drug problem. 

Photochemistry is the study of the chemical reactions and physical changes that result from interactions between matter and visible or ultraviolet light. 

There have been a number of improvements in techniques, and more convenient models have been formulated however, the basic approach of the pseudopotential total energy method has not changed. This general approach or standard modd is applicable to a broad spectrum of solid state problems and materials when the dec-trons are not too localized. Highly correlated electronic materials require more attention, and this is an area of active current research. However, considering the extent of the accomplishments and die range of applications (see Table 14.3) to solids, dusters, and molecules, this approach has had a major impact on condensed matter physics and stands as one of the pillars of the fidd. 

Finally, it is possible to produce aerosols by vaporization of solids and subsequent condensation, which under certain conditions may yield uniform spherical particles as shown on examples of NaCl (19-23), AgCl (24-26), V2Os (27), etc. It is quite apparent that all these techniques are based on physical changes of the matter that do not involve chemical reactions, while the emphasis in this chapter is on using the described aerosol technique to produce inorganic materials, in particular metal oxides and polymers, by chemical processes. 

Chang LL (1992) In Esaki L (ed) Highlights in condensed matter physics and future prospects. Plenum, New York, p 83... 

FIGURE 6.7 (a) The altitude of a location on a mountain is like a state property it does not matter what route you take between two points, the net change in altitude is the same, (b) Enthalpy is a state property if a system changes from state A to state B (as depicted highly diagrammatically here), the net change in enthalpy is the same whatever the route—the sequence of chemical or physical changes— between the two states. 

This is a short but critically important section. When a system is at equilibrium, it has no tendency to change in either direction (forward or reverse) and will remain in its state until it is disturbed from outside the system. For example, when a block of metal is at the same temperature as its surroundings, it is in thermal equilibrium with them, and energy has no tendency to flow into or out of the block as heat. When a gas confined to a cylinder by a piston has the same pressure as the surroundings, the system is in mechanical equilibrium with the surroundings, and the gas has no tendency to expand or contract (Fig. 7.21). When a solid, such as ice, is in contact with its liquid form, such as water, at certain conditions of temperature and pressure (at 0°C and 1 atm for water), the two states of matter are in physical equilibrium with each other, and there is no tendency for one form of matter to change into the other form. Physical equilibria, which include vaporization as well as melting, are dealt with in detail in Chapter 8. When a chemical reaction mixture reaches a certain composition, it seems to come to a halt. A mixture of substances at chemical equilibrium has no tendency either to produce... 

A common and important problem in theoretical chemistry and in condensed matter physics is the calculation of the rate of transitions, for example chemical reactions or diffusion events. In either case, the configuration of atoms is changed in some way during the transition. The interaction between the atoms can be obtained from an (approximate) solution of the Schrodinger equation describing the electrons, or from an otherwise determined potential energy function. Most often, it is sufficient to treat the motion of the atoms using classical mechanics,... 

Many systems of color have been developed over time. Early theories about the nature of color existed in many countries of the ancient world. An interest in color was expressed by the Babylonians as early as 1900 B.C. Most early theories assumed that color was one of the properties of matter, such as density or mass. These theories were correct in identifying some physical properties of matter. Color and density are intensive physical properties. They remain constant regardless of amount. Mass, on the other hand, is an extensive physical property of matter. It changes with amount. 

Matter is something that takes up space and has mass. Physical properties are used to describe matter. Some physical properties of matter are shape, size, amount, density, distribution, and color. A physical change is a change in a physical property without a change in the actual substance. 

In this example the standard heat of formation of H20 is available for its hypothetical standard state as a gas at 25°C. One might expect the value of the heat of formation of water to be listed for its actual state as a liquid at 1 bar or l(atm) and 25°C. As a matter of fact, values for both states are given because they are both frequently used. This is true for many compounds that normally exist as liquids at 25°C and the standard-state pressure. Cases do arise, however, in which a value is given only for the standard state as a liquid or as an ideal gas when what is needed is the other value. Suppose that this, were the case for the preceding example and that only the standard heat of formation of liquid H20 is known. We must now include an equation for the physical change that transforms water from its standard state as a liquid into its standard state as a gas. The enthalpy change for this physical process is the difference between the heats of formation of water in its two standard states ... 

A change of state alters the appearance of matter. The composition of matter remains the same, however, regardless of its state. For example, ice, liquid water, and water vapour are all the same kind of matter water. Melting and boiling other kinds of matter have the same result. The appearance and some other physical properties change, but the matter retains its identity—its composition. Changes that affect the physical appearance of matter, but not its composition, are physical changes. 

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