Specific heat alkanes

In this problem, we correlate the specific heats of normal alkanes from Cl to Ce with the number of vibrational degrees of freedom. Locate the appropriate coefficients that describe empirically the temperature dependence of the specific heat for normal alkanes from methane to n-hexane. The polynomial expression can be written genericaUy in the form... 

SPECIFIC HEATS OF LIQUID N-ALKANES. AKHMEDOVAG ZH FIZ KHIM... 

The melting temperatures of the n-alkanes were compiled by Broadhurst(17) The other parameters necessary to perform the analysis are also available. The value of AHa has been obtained by independent methods.(19) A satisfactory estimate of ACp can be made from specific heat measurements of the n-alkanes. The major objective of this analysis is to determine the value of from the melting point data of the -alkanes. 

A constant, = breakdown field, t = pulse length, m = mass of liquid, Cp ss specific heat, = boiling point, ambient temperature, and 1 = heat of vaporization. The dependence on pressure and molecular structure (which change the boiling point of liquids) fitted well with this theory. These results were, however, limited to a series of alkanes, and there is no experimental proof that bubble generation is the effective mechanism. 

If the heat of fonnation parameters are derived on the basis of fitting to a large variety of compounds, a specific set of parameters is obtained. A slightly different set of parameters may be obtained if only certain strainless molecules are included in the parameterization. Typically molecules like straight chain alkanes and cyclohexane are defined as strainless. Using these strainless heat of formation parameters, a strain energy may be calculated as illustrated in Figure 2.14. 

Dewaxing is an important specific hydrocracking process used to improve diesel and heating oils by pour-point reduction.88 This is achieved by shape selectivity of certain zeolites allowing selective hydrocracking of long-chain paraffinic waxes to C3—C5 alkanes in the presence of other paraffins.89 Platinum H-mordenite is used in an industrial process.90... 

Initially, we will be concerned with the physical properties of alkanes and how these properties can be correlated by the important concept of homology. This will be followed by a brief survey of the occurrence and uses of hydrocarbons, with special reference to the petroleum industry. Chemical reactions of alkanes then will be discussed, with special emphasis on combustion and substitution reactions. These reactions are employed to illustrate how we can predict and use energy changes — particularly AH, the heat evolved or absorbed by a reacting system, which often can be estimated from bond energies. Then we consider some of the problems involved in predicting reaction rates in the context of a specific reaction, the chlorination of methane. The example is complex, but it has the virtue that we are able to break the overall reaction into quite simple steps. 

Nanomaterial growth can be controlled by selective microwave heating as exemplified by the synthesis of CdSe and CdTe in microwave transparent alkane solvents. The high microwave absorptivity of the chalcogenide precursors allowed instantaneous activation and subsequent nucleation and is a clear example of the specific microwave effect. Regardless of the desired size, narrow dispersity nanocrystals could be isolated in less than 3 min. The reaction did not require a high temperature injection step, a problem encountered with conventional approaches. In addition, the use of a stop-flow reactor allowed for automation of the process for scale-np. 

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