Gases microscopic view

Internal Energy of Ideal Gases Microscopic View... 

A gas, at the macroscopic level, has neither a definite shape nor volume. It expands to fill its container. The microscopic view is that the particles are far apart, moving rapidly with respect to each other, and act independently of each other. 

Figure 7.10 Microscopic view of the three-phase contact region for a repulsive force between the solid-liquid and liquid-gas interface (A) and an attractive force between the two interfaces...

The vessel is shown by CDEF in Fig. la. The walls CD, DE, EF, and FC are assumed to be freely movable, but kept in the positions by forces on both sides of each of the walls. The pressure exerted by the liquid or the vapor on both sides of the walls is equal to the saturation pressure of the vapor except at the positions where the transition layer is in contact with the wall. In Fig. lb, a macroscopic view near the surface of the liquid is shown. AB is the boundary between the. liquid and the gas phases. In Fig. lc a microscopic view is shown. Consider a portion between the two planes AA and BB in the vessel. The lower part of this portion is filled with liquid while the upper part is filled with the saturated vapor. The density varies continuously from the value appropriate to the liqqid in bulk to the value of the saturated vapor. The pressure inside the walls varies continuously as the transition layer is traversed, being lower than the pressure of the saturated vapor in the transition zone. Thus it is necessary to exert tensions on the outer sides of AA and BB in order to maintain the shape of the vessel. 

The book begins with an elementary but rigorous account of the various types of forces between molecules. Chapter 2 is concerned with the hydrogen bond between pairs of simple molecules in the gas phase, with particular reference to the preferred relative orientation of the pair and the ease with which this can be distorted. This microscopic view continues in chapter 3 wherein the nature of interactions between solute molecules and solvents or between two or more solutes is examined from the experimental standpoint, with various types of spectroscopy providing the probe of the nature of the interactions. 

However, if an LC substance is heated, it will show more than one melting point. Thus, liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid and a solid crystal. For instance, an LC may flow like a liquid but have the molecules in the liquid arranged and/or oriented in a crystal-like way. There are many different types of LC phases that can be distinguished based on their different optical properties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have a distinct texture. Each patch in the texture corresponds to a domain where the LC molecules are oriented in a different direction. Within a domain, however, the molecules are well ordered. Liquid crystal materials may not always be in an LC phase (just as water is not always in the liquid phase it may also be found in the solid or gas phase). 

The laser ablation system consists of a high-power pulsed laser, optics to focus the laser at or near the surface of the sample, and an ablation cell. Small ablated particles are swept out of the ablation cell and carried into the ICP in a flowing gas. Often a microscope lens and video camera are positioned to allow the operator to view the sample surface before and after ablation. A high-quality microscope and precise positioning of the sample relative to the laser beam are essential for good spatially resolved sampling. 

A second way to visualize gas behavior is by considering the gas to be a continuous medium, i.e., similar to some sort of interlocking syrup such as molasses or water. Study of medium properties in this case is known as fluid dynamics or for air aerodynamics. In the first case, the microscopic (small) properties of the gas are important. In the second, it is the macroscopic (large) properties which are of interest. Since aerosol particles can span the range from near-molecular sizes up to hundreds of micrometers, the gas in which the particles are suspended must be considered both from a molecular point of view and as a continuous medium. 

---