NIST Webbook

Polyatomic molecules vibrate in a very complicated way, but, expressed in temis of their normal coordinates, atoms or groups of atoms vibrate sinusoidally in phase, with the same frequency. Each mode of motion functions as an independent hamionic oscillator and, provided certain selection rules are satisfied, contributes a band to the vibrational spectr um. There will be at least as many bands as there are degrees of freedom, but the frequencies of the normal coordinates will dominate the vibrational spectrum for simple molecules. An example is water, which has a pair of infrared absorption maxima centered at about 3780 cm and a single peak at about 1580 cm (nist webbook). 

NIST Webbook, http //webbook.nist.gov/chemistry. http //i-systems,dechema.de/detherm.datasets.php ... 

The NIST Webbook gives data for heat capacity over a range of temperatures, and it provides coefficients for empirical equations for heat capacity as a function of temperature for solid, liquid, and gas phases. The latter are referred to as Shomate equation parameters. ... 

Figure 9.1. Volume of a pure phase at specified temperature and pressure. Data for water at 273.16 K and 100 kPa from the NIST WebBook on saturation properties for water, (http // www.webbook.nist.gov/chemistry)...

NIST WebBook. http //www.WebBook.nist.gov/cheinistry. 

The Wlc total atomization energy at 0 K of aniline, 1468.7 kcal/mol, is in satisfying agreement with the value obtained from heats of formation in the NIST WebBook 39), 1467.7 0.7 kcal/mol. (Most of the uncertainty derives from the heat of vaporization of graphite.) The various contributions to this result are (in kcal/mol) SCF limit 1144.4, valence CCSD correlation energy limit 359.0, connected triple excitations 31.7, inner shell correlation 7.6, scalar relativistic effects -1.2, atomic spin-orbit coupling -0.5 kcal/mol. Extrapolations account for 0.6, 12.1, and 2.5 kcal/mol, respectively, out of the three first contributions. 

CHASE, M. W. 1998. NIST-JANAF Thermochemical Tables, 4th edn. J. Phys. Chem. Ref. Data, Monograph 9, 1-1951. Cited in US National Institute of Standards and Technology (NIST) Webbook, http //webbook.nist.gov. 

Even though InChl is a relatively new format (the first stable version of the InChl software was published in 2005), it has already gained broad acceptance in the chem-informatics world. It is supported by most of the major chemical drawing programs and is used in such databases as PubChem (http //pubchem.ncbi.nlm.nih.gov/) and NIST Webbook (Linstrom and Mallard 2005). 

National Institute of Standards and. r - Technology (NIST) WebBook... 

Table 2. Donor qualities (HOMO energies) of a variety of a, experimental ionization energies from the NIST webbook [5], n, and n donors as determined by...

NIST Webbook http //webbook.nist.gov/chemistry. 

Bond enthalpies from Kerr s tables95 and data in the NIST WebBook. 

Since the IP of hydrogen is a constant equal to 313.6 kcal/mol [16], the enthalpy change A// , depends basically on the difference between the bond dissociation energy D iA—H), and the electron affinity EA(A). For many years the experimental way of obtaining AH for a compound was from dissociation energies and electron affinity measurements. For an interesting explanation of details of such procedures, see Bartmess and Mclver [17] and Lias and Bartmess [18]. A more recent and comprehensive discussion of the various experimental techniques available for measuring these properties can be found in the NIST webbook [18]. 

One of the more useful free resources on the Internet for analytical chemists is the NIST WebBook http //webbook.nist.gov. The WebBook can be searched through a number of keys but unfortunately spectral searching is not one of them ... 

One of the most useful features of the NIST WebBook we have found is the name search, where a large selection of alternative names for a particular compound are available and searchable, greatly increasing the chance of finding the information you want on a particular substance of you do not know the lUPAC or CAS name or the CAS registry number and are not reaUy too sure of the chemical structure. However it is possible to upload chemical structures for example (Fig. 24.5). 

Based on average bond energy of ZrF4 in NiST Webbook. 

Solution We use the NIST WebBook for the properties of ammonia. We will set the evaporator at - 22 °C, 2 °C below the required temperature. The saturation pressure at this temperature is 1.7379 bar. The condenser uses air at 26 °C as the cooling medium. Allowing for a 2 °C temperature difference, the temperature at the exit of condenser must be at least 28 °C. This corresponds to saturation pressure 10.993 bar and sets the compression pressure of the cycle. Thus we have determined the two pressures of the cycle. We set the state at the exit of the condenser to be saturated liquid, and at the exit of the evaporator to be saturated vapor. With reference to Figure 6-12. the states of streams 1 and 3 are fixed (saturated phases at known pressure) and their properties are shown below (also notice that the pressure of all streams are known). 

Compressor. It will be convenient to use the NIST WebBook to tabulate enthalpy and entropy at 10.993 bar over small increments of temperature. This will facilitate the interpolations needed in the calculation of the compressor. The following data were obtained at 20 "C increments ... 

Solution We will use the NIST WebBook to calculate the properties of nitrogen. The pressures of all streams are known streams 1, 2, 6, 7, 8, and 9 are at 1 bar streams 3,4, and 5 are at 180 bar. Streams 6,7, and 8 is the boiling temperature of nitrogen at 1 bar (-195.91 °C). We notice now that the state of streams 1,7,8, and 9 is fully defined and their properties may be collected from the Webbook (see summaiy table below). In addition to the usual properties (P, T, H, S, and phase) we must also include in the table of streams the flow rates, since these are not the same among all streams. We set the basis to be 1 kg of liquid nitrogen in stream 7, and the unknown flow rate of vapor stream 8 to be x. By straightforward material balance, the flow rate of stream 1 is 1 kg/s, the flow rate of streams 8 and 9 are x, and all other flow rates are x + 1. The known properties of the streams are summarized below ... 

From the NIST WebBook at 25 °C, 3 bar kg/mol. With this value we find... 

The NIST WebBook site [73] prefers the Shomate polynomials [80], which are defined in the following way with the coefficients A-H ... 

Data from the compilation by Bartmess, J. E. in Mallard, W. G. Linstrom, P. J., Eds. NIST Webbook, NIST Standard Reference Database Number 69 National Institute of Standards and Technology Gaithersburg, MD (http //webbook.nist.gov). 

Our best theoretical values suggest that the experimental gas-phase heats of formation from the NIST WebBook should be revised downward by 2.4 (alanine), 0.7-0.8 (glycine), 3.2 (methionine), and 5.3 (proline) kcal/mol. Similarly, we suggest that the experimental values from the... 

The type of calculation shown in the previous example has occasional application the Handbook of Chemistry in chemistry. But Hess s law is also useful in another more common approach, and Phys cs, or in online source Heats of formation for many substances are widely tabulated (see Appendix E). such as the NIST WebBook. 

While many earlier compilations of data have used the Electron Convention, the most recent tabulation of standard enthalpies described in the NIST Webbook (http //www.nist.gov) employs the Ion Convention. It does not introduce any temperature dependence, however small, to ion enthalpies of formation and is, therefore, considered a simpler and less confusing representation of data. This convention is also consistent with the literature of the ion physics and chemistry community over the past 50 years. In any application of tabulated thermochemical data, investigators are cautioned to be exceedingly clear about the conventions of the data they employ. 

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