Thermodynamics molecular interpretation

Equation (16-2) allows the calculations of changes in the entropy of a substance, specifically by measuring the heat capacities at different temperatures and the enthalpies of phase changes. If the absolute value of the entropy were known at any one temperature, the measurements of changes in entropy in going from that temperature to another temperature would allow the determination of the absolute value of the entropy at the other temperature. The third law of thermodynamics provides the basis for establishing absolute entropies. The law states that the entropy of any perfect crystal is zero (0) at the temperature of absolute zero (OK or -273.15°C). This is understandable in terms of the molecular interpretation of entropy. In a perfect crystal, every atom is fixed in position, and, at absolute zero, every form of internal energy (such as atomic vibrations) has its lowest possible value. 

It is therefore remarkable that 100 years or so before the laws of thermodynamics were formulated, Daniel Bernoulli developed a billiard ball model of a gas that gave a molecular interpretation to pressure and was later extended to give an understanding of temperature. This is truly a wonderful thing, because all it starts with is the assumption that the atoms or molecules of a gas can be treated as if they behave like perfectly elastic hard spheres—minute and perfect billiard balls. Then Newton s laws of motion are applied and all the gas laws follow, together with a molecular interpretation of temperature and absolute zero. You have no doubt... 

Over a long period of time experimental results on amphiphilic monolayers were limited to surface pressure-area ( r-A) isotherms only. As described in sections 3.3 and 4, from tc[A) Isotherms, measured under various conditions, it is possible to obtain 2D-compressibilities, dilation moduli, thermal expansivities, and several thermodynamic characteristics, like the Gibbs and Helmholtz energy, the energy cmd entropy per unit area. In addition, from breaks in the r(A) curves phase transitions can in principle be localized. All this information has a phenomenological nature. For Instance, notions as common as liquid-expanded or liquid-condensed cannot be given a molecular Interpretation. To penetrate further into understanding monolayers at the molecular level a variety of additional experimental techniques is now available. We will discuss these in this section. 

Pressure-area ( r(A)) isotherms Phase transitions, packing densities, compressibilities, thermodynamic cheiracteristics. Molecular Interpretation very limited. 

Boltzmann s molecular interpretation compared with the thermodynamic approach... 

In assessing the meaning of the parameters y and 3j/dT, one eventually asks the question What is the interface and how thick is it The interface certainly has the thickness of the layer of molecules at the termination of the liquid phase but the disruption of normal liquid structure may extend somewhat further into the bulk. Since the thickness of the interface is not known, it is difficult to give a molecular interpretation of the thermodynamic properties of this region. However, effective thermodynamic conventions have been developed for discussing interfacial properties. These are outlined in detail in the following section. 

The molecular interpretation of thermodynamic data of temperature and pressure effects on proteins and their reactions is based on the data obtained from small molar mass model compounds in water. Weber and Drickamer [75] have pointed out the role of mechanical effects on the volume of association of molecular complexes by introducing molecular spacers that prevent molecules to get in close contact. As can be seen from Table 2, these mechanical effects can show up considerably in the volume changes, ft is clear that such effects should also influence hydrophobic interactions in proteins. 

Thermodynamics is a macroscopic science that deals with such properties as pressure, temperature, and volume. Unlike quantum mechanics, thermodynamics is not based on a specific model, and therefore it is unaffected by our changing concepts of atoms and molecules. By the same token, equations derived from thermodynamics do not provide us with molecular interpretations of complex phenomena. Furthermore, thermodynamics tells us nothing about the rate of a process except its likehhood. 

What is the molecular interpretation of the dependence of the thermodynamic energy on the volume ... 

Aqueous Solvation.—A review, covering the 1968—1972 publications, deals with physical properties, thermodynamics, and structures of non-aqueous and aqueous-non-aqueous solutions of electrolytes, and complete hydration limits. Thermodynamic aspects of ionic hydration also reviewed include the thermodynamic theory of solvation the molecular interpretation of ionic hydration hydration of gaseous ions (AG s, H s, and AA s) thermodynamic properties of ions at infinite dilution in water, solvent isotope effect in hydration reference solvents and ionic hydration and excess properties. A third review on the hydration of ions emphasizes the structure of water in the gaseous, liquid, and solid states the size of ions and the hydration numbers of ions and the structure of the hydrated shell from measurements of mobility, compressibility, activity, and from n.m.r. spectra. Pure water and aqueous LiCl at concentrations up to saturation have been examined by neutron and X-ray diffraction. For the neutron studies LiCl and D2O are employed. The data are consistent with a simple model involving only... 

So far the equilibria between phases have been considered in the light of thermodynamic principles. These, of course, are only a formal embodiment of the statistical laws governing the behaviour of large numbers of particles, and the major results which they predict should be interpretable directly in terms of the molecular-kinetic picture. Though sometimes more difficult to carry through in detail, the molecular interpretations are of considerable interest in themselves. All are variations on the familiar theme that the random motions of the molecules tend by themselves to dissipate matter into the state of rarefied gas, while attractive forces tend to collect it into... 

Mark, J.E., 1973. Thermoelastic properties of rubberlike networks and their thermodynamic and molecular interpretation. Rubber Chem. Technol. 46, 593. 

The first molecular interpretation was attempted by Eley (1939, 1944). Eley assumed that the process of solution can be viewed as a two-step process first, the creation of a cavity that can accommodate the solute, and second, the introduction of the solute into this cavity. Thus, schematically, the process is depicted in Fig. 3.1. For each thermodynamic quantity of solution, say the standard enthalpy and entropy, one can write... 

As the extent of reaction is a thermodynamic variable, the general definition of the rate of reaction as dX/dt is also a thermodynamic quantity and indeed it plays a central role in the thermodynamics of irreversible processes. Being a thermodynamic quantity, it is totally unrelated to any molecular interpretation as to how the chemical reaction actually otcurs. In particular, the definition applies to any single reaction, i.e., one the advancement of which... 

THE MOLECULAR INTERPRETATION OF ENTROPY AND THETHIRD LAW OFTHERMODYNAMICS On the molecular level, we learn that the entropy of a system is related to the number of accessible microstates. The entropy of the system increases as the randomness of the system increases. The third law of thermodynamics states that, at 0 K, the entropy of a perfect crystaiiine soiid is zero. 

SECTION 19.3 The Molecular Interpretation of Entropy and the Third Law of Thermodynamics... 

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