Gaseous Heat Capacities Research Articles

A Possible Explicit Equation Fitting Method for the Gaseous Heat Capacity Near the Critical Point Based on Density and Temperature

CO2 is a potential fluid for absorbing and accumulating thermal energy; an accurate and fast calculation method for the heat capacity is essential for the study of the flow state near the critical point. However, the calculation of the heat capacity near the critical point by the equations suggested by NIST can easily be divergent, such as for CO2, nitrogen, methane, etc. Therefore, an explicit fitting equation was studied. The fitting equation, which used density and temperature as variables and contained three constants, was derived from the nature of heat capacity change (molecular kinetic energy and potential energy). Based on the heat capacity data of the NIST WebBook, the heat capacity of CO2 is taken as the example for the equation deduction and parameter fitting. The three constants were defined in order by Origin fitting software. By this new approach, it is found that the heat capacity at the critical point is below 1% deviant from that of the NIST WebBook. Moreover, the heat capacities that are difficult to be calculated in the NIST WebBook are well calculated. The study shows that the fitting equation is efficient for the prediction of heat capacity of gases near the critical point.

Features of the thermodynamic properties of gaseous and solid methane

A detailed analysis and calculation of the rotational component of the heat capacity of gaseous and solid methane is carried out. Correction of the generally accepted estimates of the contribution of quantum effects to the rotational heat capacity of methane in both gaseous and solid state is performed.

Measurement of Isobaric Heat Capacity of Gaseous Trans-1,3,3,3-tetrafluoropropene (HFO 1234ze (E) )

The specific isobaric heat capacity (cp) was measured for HFO-1234ze(E) (trans-1,3,3,3-tetrafluoropropene) in the gas phase. HFO-1234ze(E) has a lower GWP value of 6 and is one of new environment-friendly refrigerants. Nineteen measurements for HFO-1234ze(E) were obtained at temperatures from 303 K to 363 K and at pressures from 0.35 to 1.3 MPa. The expanded uncertainty (k= 2) of the temperature measurements is estimated to be less 22 mK, and that of the pressure measurements is less 4.4 kPa. The expanded uncertainty for cp is estimated to range from 14 to 21 J/kg.K.

A Classical and Quantum Chemical Analysis of Gaseous Heat Capacity

Physical chemistry is considered to be a scientifically abstract and mathematically intensive course in the undergraduate chemistry curriculum. To most students, the physical chemistry course involves a semester that deals with macroscopic properties and another that deals with microscopic evaluations of chemical systems. They often fail to see the importance of statistical mechanics in making the connection between the content of the two semesters. In this paper, we propose a computational exercise that complements a simple physical chemistry experiment that can be used to understand the chemical basis of a macroscopic property such as the heat capacity of gases using microscopic (classical and quantum) mechanics. Students are given the opportunity to use (1) computational chemistry software to calculate the contributions of translational, rotational, and vibrational motion to the energy of molecules; (2) a graphing program to study the linear and nonlinear dependence of energy on temperature; (3) classical, quantum, and statistical mechanical theory to verify experimental data; (4) regression analysis to approximate the heat capacity constant of simple gases from energy calculations.

Heats of vaporization and gaseous molar heat capacities of ethanol and the binary mixture of ethanol and benzene

A combined system of the Newsham vaporization calorimeter and the Pitzer gaseous heat capacity flow calorimeter were reconstructed with modifications. Both calorimeters were calibrated with benzene, the liquid standard, and were found to be acceptable for measurements, with deviations of 0.4% and 0.9%, respectively. Heats of vaporization of pure ethanol under five pressures and binary mixtures of ethanol and benzene under normal pressure were determined. Gaseous molar heat capacities of pure ethanol under three pressures and of binary mixture of ethanol and benzene at two temperatures were also determined, with anomalies due to association noted. Association of ethanol molecules in the vapor phase was discussed and analyzed, with heats of association and entropy change of association calculated.

Spectroscopic Studies of Rotational Isomerism. III. The Normal Paraffins in the Liquid and Solid States

The Raman spectra of n-butane, n-pentane, n-hexane, and n-heptane have been investigated in the liquid phase between 310°K and their melting points, and also in the solid phase. The room temperature spectra clearly show the presence of appreciable concentrations of two rotational isomers in butane and pentane, and of three isomers in hexane and probably in heptane. In the solid phase only one of these isomers is present, and in agreement with previous conclusions based on spectroscopic and other evidence, this lowest energy form was assumed to possess the planar, trans-, zig-zag configuration. The spectra of the solids yield experimental values for the limiting skeletal stretching frequencies of the zig-zag form, and these were compared with values calculated by previously established methods. The photoelectric spectrograph was used for quantitative intensity measurements on selected line pairs of each molecule over appropriate temperature intervals, and from the results values were obtained for the energy difference, —ΔH, between rotational isomers. The values obtained were 760±100 cal. mole−1 in n-butane, 450±60 cal. mole−1 in n-pentane, 520±70 and 470±60 cal. mole−1 in n-hexane. No quantitative result could be obtained for n-heptane. The observed gaseous heat capacities of n-butane, n-pentane, and n-hexane were compared with values calculated by statistical mechanics. It was found that for n-pentane and n-hexane the calculated values do not agree accurately with the experimental results, probably because of the simplified partition functions used to obtain the compositions of the isomeric mixtures.

Spectroscopic Studies of Rotational Isomerism. IV. 2-Methyl Butane and 2,3-Dimethyl Butane

The Raman spectra of 2-methyl butane and 2,3-dimethyl butane were investigated between room temperature and 90°K. In marked contrast to the behavior of the normal paraffins all the main lines persist in the solid phase. The slight change with temperture in the relative intensity of one line pair in liquid 2-methyl butane was investigated quantitatively with the photoelectric spectrograph. No measurable intensity changes were observed in the 2,3-dimethyl butane spectrum. The results were interpreted in terms of both a very small (<100 cal. mole−1) and a very large (1600 cal. mole−1) energy difference between the rotational isomers. Although both interpretations appear consistent with the spectroscopic results, neither affords a completely straightforward explanation of all the facts. It is shown for 2-methyl butane that accurate gaseous heat capacities would distinguish between these alternatives. The spectroscopic data on 2,3-dimethyl butane are inconsistent with a single molecular configuration possessing a center of symmetry.

The Measurment of Gaseous Heatcapacities of Organic Substances by the “Hot Wire Method.” II

The Measurment of Gaseous Heatcapacities of Organic Substances by the “Hot Wire Method.” II

The Measurement of Gaseous Heatcapacities of Organic Substances by the “Hot Wire Method.” I

The Measurement of Gaseous Heatcapacities of Organic Substances by the “Hot Wire Method.” I

On the Gaseous Heat Capacities of Ethylene Dichloride and the Acoustical Velocities in that Vapour

On the Gaseous Heat Capacities of Ethylene Dichloride and the Acoustical Velocities in that Vapour

An Improved Apparatus for Supersonic Velocity and Absorption Measurements

The value and uses of supersonic velocity and absorption measurements are reviewed, and evidence that sound velocity measurements may still be used for heat capacity determinations is presented. An apparatus which is designed for (1) a general study of acoustical dispersion, and (2) the supersonic measurement of gaseous heat capacities. The general experimental technique to be used with such an apparatus is outlined, and results of measurements of the velocity of sound in air and of the heat capacity of propylene are briefly discussed.

Supersonic Measurement of the Heat Capacity of Propylene

An apparatus designed for (1) a general study of acoustical dispersion in gases, and (2) measurement of gaseous heat capacities has been used to measure the heat capacity of propylene between 273 and 490°K. The general methods used are outlined and discussed. The measured heat capacity values agree well with those calculated from the frequency assignment as given by Wilson and Wells, and an assumed potential restricting rotation of about 2000 cal./mole, but deviate from the values calculated from Pitzer's frequency assignment and an 800-cal./mole potential. The measurements on propylene also have the value of serving as a test of the usefulness and practicality of the supersonic method of heat capacity determinations.

The Gaseous Heat Capacity and Restricted Internal Rotation of Diborane

The heat capacity of gaseous diborane has been measured from 95° to 324°K with the low pressure thermal conductivity apparatus described earlier. The bracketing method was applied over most of this temperature range, with acetylene and ethylene as comparison gases. At 95°K, ethylene and ethane were used as comparison gases and the accommodation coefficient ratios were assumed to be unity. The heat capacity at low temperatures indicates that internal rotation in the diborane molecule is restricted by a potential barrier whose height is probably between 4000 and 6000 cal./mole if the barrier is assumed to be a sinusoidal function of the internal rotational angle.

The Low Temperature Gaseous Heat Capacities of Certain C3 Hydrocarbons

The low pressure thermal conductivities of allene, propylene, propane, methyl acetylene and cyclopropane have been measured over the temperature range 150 to 340°K. The heat capacities derived from these measurements are compared with those from other sources. Data are presented in support of the bracketing method for deriving heat capacities from heat conductances. Heats of certain hydrogenation reactions, when calculated to 0°K and to the nonvibrating state, are found to exhibit the same regularities as the experimental values determined at 335°K.

Gaseous Heat Capacities. III

The present paper presents a continuation of measurements on the gaseous heat capacities by the adiabatic expansion method. The apparatus and the experimental procedure are exactly the same as described in the previous papers denoted herein as Part I and Part II. The compounds with which the present paper deals are dimethyl ether, ethylene oxide, dimethyl acetylene, cis-butane-2 and trans-butene-2. For the correction of the experimental data to the ideal gas state several procedures had to be used, as discussed in Part II.

Gaseous Heat Capacities. II

The present paper describes a continuation of the work on the heat capacities of lower hydrocarbons by the Lummer-Pringsheim adiabatic expansion method. The apparatus and the procedure described in the first paper of this series, henceforth to be denoted as Part I, was used in the present research without important modifications.

Gaseous Heat Capacities I. The Method and the Heat Capacities of C2H6 and C2D6

An apparatus is described for the adiabatic expansion method of Lummer and Pringsheim, new features of which are a device for accurate and rapid pressure measurements and an effective design of the expansion vessel. The Wollaston wires, serving as a resistance thermometer, are subjected to extensive heat treatment which stabilizes their electrical characteristics so well that resistance changes accompanying gas expansion can be translated into temperature changes by means of separately determined temperature coefficients of resistance. The method here described is thus an absolute one and is not dependent on comparison with other gases of known heat capacity. Causes of imperfect temperature constancy after expansion are quantitatively discussed and traced to two processes: the heat conduction by the gas and the absorption of thermal radiation from the walls by the gas. Experimental data on air and carbon dioxide are presented and are compared with the theoretical values. Heat capacities of C2H6 and C2D6 are reported for the interval 0 to 90°C.

The Low Temperature Gaseous Heat Capacities of C2H6

The heat capacities of gaseous C2H6 and C2D6 have been measured down to 93°K with the low pressure thermal conductivity apparatus previously described. An improved cryostat and better designed conductivity cells were used. A new method of obtaining the heat capacities from the thermal conductivity data is described which does not require a knowledge of the accommodation coefficient α. It is based on the assumption that when the accommodating efficiency of the wire is changed, α changes in the same direction for the gases being compared and further that the percentage change in α is greater the more its absolute value deviates from unity. It is then possible to show that the unknown α for the gas being studied can be bracketed within narrow limits by the α's of comparison gases. The heat capacity results for light and heavy ethane indicate a potential barrier restricting internal rotation of essentially sinusoidal shape and with a depth of 2750 cal./mole.