Macroscopic properties boiling point

The thermodynamic state is therefore considered equivalent to specification of the complete set of independent intensive properties 7 1 R2, Rn. The fact that state can be specified without reference to extensive properties is a direct consequence of the macroscopic character of the thermodynamic system, for once this character is established, we can safely assume that system size does not matter except as a trivial overall scale factor. For example, it is of no thermodynamic consequence whether we choose a cup-full or a bucket-full as sample size for a thermodynamic investigation of the normal boiling-point state of water, because thermodynamic properties of the two systems are trivially related. 

PhysChem Batch Advanced Chemistry Development Inc. www.acdlabs.com pKa, log Kow, log D, K c, bioconcentration factor, solubility at a certain pH, boiling point, vapor pressure, enthalpy of vaporization, flash point, macroscopic properties... 

When a molecule takes part in a reaction, it is properties at the molecular level which determine its chemical behaviour. Such intrinsic properties cannot be measured directly, however. What can be measured are macroscopic molecular properties which are likely to be manifestations of the intrinsic properties. It is therefore reasonable to assume that we can use macroscopic properties as probes on intrinsic properties. Through physical chemical models it is sometimes possible to relate macroscopic properties to intrinsic properties. For instance 13C NMR shifts can be used to estimate electron densities on different carbon atoms in a molecule. It is reasonable to expect that macroscopic observable properties which depend on the same intrinsic property will be more or less correlated to each other. It is also likely that observed properties which depend on different intrinsic properties will not be strongly correlated. A few examples illustrate this In a homologous series of compounds, the melting points and the boiling points are correlated. They depend on the strengths of intermolecular forces. To some extent such forces are due to van der Waals interactions, and hence, it is reasonable to assume a correlation also to the molar mass. Another example is furnished by the rather fuzzy concept nucleophilicity . What is usually meant by this term is the ability to donate electron density to an electron-deficient site. A number of measurable properties are related to this intrinsic property, e.g. refractive index, basicity as measured by pK, ionization potential, HOMO-LUMO energies, n — n ... 

The aforementioned macroscopic physical constants of solvents have usually been determined experimentally. However, various attempts have been made to calculate bulk properties of Hquids from pure theory. By means of quantum chemical methods, it is possible to calculate some thermodynamic properties e.g. molar heat capacities and viscosities) of simple molecular Hquids without specific solvent/solvent interactions [207]. A quantitative structure-property relationship treatment of normal boiling points, using the so-called CODESS A technique i.e. comprehensive descriptors for structural and statistical analysis), leads to a four-parameter equation with physically significant molecular descriptors, allowing rather accurate predictions of the normal boiling points of structurally diverse organic liquids [208]. Based solely on the molecular structure of solvent molecules, a non-empirical solvent polarity index, called the first-order valence molecular connectivity index, has been proposed [137]. These purely calculated solvent polarity parameters correlate fairly well with some corresponding physical properties of the solvents [137]. 

Solvents can have a significant effect on the outcome of chemical reactions and physical chemical processes including extractions and crystallizations. Both the macroscopic (boiling point, density) and microscopic (dipole moment, hydrogen bonding ability) properties of the solvent affect its influence on such processes and the choice of solvent for a chemical system. For most paints and inks... 

Table 3 contains the physical properties of solvents that are used for dissolving alkali metals. Besides boiling point (b.p.) and viscosity (the data enable one to judge on the experimental potentialities inherent in a solvent) the Table contains values of dielectric constant and of donor and acceptor numbers (DN, AN). It is hard to notice any correlation between the macroscopic properties of the solvents, on the one hand, and their ability to dissolve alkali metals and the possibility of electrochemical generation of solvated electrons, on the other hand. 

When you compare the physical properties of the polar molecule water with the nonpolar molecule methane, you see major differences. Although water and methane are approximately the same size and both are covalently bonded, water is a liquid at room temperature, whereas methane is a gas. Table 9.2 shows a comparison of the melting points and boiling points of water and methane. Notice that the boiling point of water is 264°C higher than the boiling point of methane. This is macroscopic evidence for the submicroscopic attractions at work among water molecules. 

For the purposes of interpreting and predicting chemical reactivity, a b initio Hartree-Fock computations are often quite satisfactory. These yield one-electron properties, such as the molecular electrostatic potential, to first-order accuracy [1-5], which frequently suffices to identify, for example, sites for electrophilic and/or nucleophilic attack [2, 5], Quantities related to the electrostatic potential on the molecular surface have also been related to a variety of condensed phase macroscopic properties, including pKa s, heats of vaporization, boiling points, critical constants, solubilities, etc. [6, 7]. 

Chemistry is devoted to the understanding of macroscopic observations in terms of molecular behavior. Chemists observe a compound with one set of physical properties and by chemical reaction transform it to another compound with a different set of physical properties, such as melting point, boiling point, density, color, odor, and spectra. Chemists explain these macroscopic properties on the basis of molecular structure, regardless of whether they observe the compound in the gas phase, as a dilute solution, or as a solid. 

Often in the course of research, however, the product of a synthesis is a new compound—one that has never been described before. In these instances, success in isolating the new compound depends on making reasonably accurate estimates of its melting point, boiling point, and solubilities. Estimations of these macroscopic physical properties are based on the most likely structure of the substance and on the forces that act between molecules and ions. The temperatures at which phase changes occur are an indication of the strength of these intermolecular forces. 

Politzer and co-workers defined several statistical quantities (such as the average MSEP, the standard deviation of the MSEP) that are calculated from the MSEP and found empirical relations between condensed-phase organic-compound macroscopic properties that depend on intermolecular interactions (such as normal boiling point, heats of fusion and vaporization, surface tension) and the MSEP quantities. This allows prediction of these macroscopic properties from the MSEP with a fair degree of success [P. Politzer and J. S. Murray, Fluid Phase Equilib., 185,129 (2001)]. 

No matter how it is defined, measured, or calculated, the polarity of molecules correlates with macroscopic properties such as density, miscibility/solubility, boiling point, melting point, critical point, retention time in chromatography, dilation capacity, and viscosity. 

In this chapter, we examined liquids and solids, states of matter held together by cohesive interactions among molecules or atoms (12.2). The structure of a molecule determines how strong these interactions will be, which in turn determines the macroscopic properties like melting point, boiling point, and volatility (12.3). 

The radius of the bubble was introduced above as if it were a well-defined quantity, but if we accept (as we must) the Poisson-Rayleigh view that the real gas-liquid surface is not sharp at a molecular level, then wc must ask precisely how we define the radius. Hie answer, at a macroscopic level of argument, is that it is the distance that makes (2.1) the correct relation between Ap and cr ( 2.4). Sudi a surface between two phases is called the surface of tension it is the second macroscc ic property, the first being the tension itself, whidi enters into the mediani-cal and thermodynamic discussion. In liquids below their normal boiling points the surface is found to be optically sharp, that is, sharp on a scale of length of 100 run or less, and the surface (d tension coincides, within this limit, with the sharp surface that is seen. 

From a macroscopic point of view, gas-solid fluidized beds may be regarded as well-stirred, boiling liquids the liquid-like properties of fluidized beds are readily shown in Fig. 7.25. 

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