Relation of the temperature derivative of heat of vaporization to the difference of heat capacities along the saturated vapour pressure curve

1981 ◽  
Vol 46 (10) ◽  
pp. 2446-2454
Author(s):  
Václav Svoboda ◽  
Zdeněk Wagner ◽  
Petr Voňka ◽  
Jiří Pick
Keyword(s):  
Heat Capacity ◽  
Vapour Pressure ◽  
Pressure Curve ◽  
Temperature Derivative ◽  
Heat Of Vaporization ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Vapour Pressure Curve ◽  
Pure Substances ◽  
The Difference

A method of calculating the heat capacity difference of liquid and its vapour along saturated vapour pressure curve is discussed. The qualitative course of this difference in dependence on temperature obtained from the data on the temperature dependence of heat of vaporization of pure substances is judged.

Equilibrium between a condensed phase and a reactive vapour: the heat capacity of a saturated, dissociating vapour and the form of the vapour pressure curve

1961 ◽  
Vol 264 (1319) ◽  
pp. 516-539
Keyword(s):  
Heat Capacity ◽  
Vapour Pressure ◽  
Equations Of State ◽  
Vapour Phase ◽  
High Heat ◽  
Pressure Curve ◽  
Degree Of Dissociation ◽  
Saturated Vapour ◽  
Vapour Pressure Curve ◽  
Large Heat

At constant pressure, the vapour of a dissociating substance has an anomalously high heat capacity C g p . The anomalous part is always positive and may be many times the ‘normal’ value for an otherwise similar, inert vapour. The saturated vapour of the same substance, however, with a heat capacity C g sat may show either a smaller anomaly in the same sense, or be entirely free from any anomaly, or show an anomaly in the opposite sense to, and even larger than, that in C g p . The factors governing the occurrence, the size and the sign of this anomaly are the degree of dissociation, and the relative magnitudes of the enthalpies of dissociation and vaporization. Expressions are derived for the heat capacities of saturated vapours for the general dissociation ( Am ^ mA ) and the particularly common case of dimerization ( A 2 ^2 A ) and their application to real substances illustrated. The influence of gas imperfections is discussed. Except in the region of the critical point (where valid, explicit equations of state are not available) the existence of non-ideality modifies the conclusions only in degree. Like the heat capacity of saturated vapour, the latent heat of vaporization and its temperature coefficient also contain anomalous, reactive contributions. The influence of these anomalies on the form of the relationship between vapour pressure and temperature is examined. It is found that, despite the existence of such a mobile equilibrium, and even in the presence of an abnormally large heat capacity of saturated vapour, the saturation line (in the form of a graph of In P against T -1 ) may show no marked curvature. Conversely, linearity of a graph of In P against T -1 is no guarantee that reactions of dimerization or polymerization are absent from a vapour phase.

Verification of the calculation of the constant-volume heat capacity difference of substances in the liquid and gas phases from the temperature dependence of heat of vaporization

1983 ◽  
Vol 48 (8) ◽  
pp. 2141-2146
Author(s):  
Věra Uchytilová ◽  
Václav Svoboda
Keyword(s):  
Heat Capacity ◽  
Temperature Dependence ◽  
Constant Volume ◽  
Heat Of Vaporization ◽  
Gas Phases ◽  
Volume Heat ◽  
Pure Substances ◽  
The Difference ◽  
Heats Of Vaporization ◽  
The Ideal

The possibilities were verified of the proposed method for calculating the difference between constant-volume heat capacities of liquids and gases in the ideal state from known data on the volumetric behaviour and temperature dependence of heats of vaporization of pure substances.

scholarly journals Enthalpy Relaxation Phenomenon of Heavy Ice

1979 ◽  
Vol 22 (86) ◽  
pp. 155-164
Author(s):  
Osamu Haida ◽  
Hiroshi Suga ◽  
Syūzō Seki
Keyword(s):  
Heat Capacity ◽  
Vapour Pressure ◽  
Activation Enthalpy ◽  
Thermal Anomaly ◽  
Adiabatic Calorimeter ◽  
Heat Capacity Data ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Relaxational Process ◽  
Capacity Data

AbstractThe heat capacities of quenched and annealed heavy ice Ih were measured in the temperature range 14 to 300 K by an adiabatic calorimeter. A relaxational thermal anomaly was found at around 115K and this phenomenon was ascribed to the onset of deuteron ordering in the crystal. The average activation enthalpy of the relaxational process was determined to be (26±5) kJ mol–1. Residual entropies of the crystal were recalculated on the basis of the present heat-capacity data combined with the revised values for enthalpy of vapourization, saturated vapour pressure, and spectroscopic entropy. They are (3.47±0.41) J K–1 mol–1 for the quenched crystal and (3.44±0.41) J K–1 mol–1 for the crystal annealed at 102–106 K for 264 h. The characteristics and the origin of the anomaly are discussed in comparison with that of ordinary ice.

Determination of heats of vaporization and some other thermodynamic properties for four substituted hydrocarbons

1982 ◽  
Vol 47 (2) ◽  
pp. 543-549 ◽  
Author(s):  
Václav Svoboda ◽  
Vladimíra Charvátová ◽  
Vladimír Majer ◽  
Vladimír Hynek
Keyword(s):  
Thermodynamic Properties ◽  
Temperature Dependence ◽  
Constant Pressure ◽  
Pressure Curve ◽  
Saturated Vapour Pressure ◽  
Vapour Pressure Curve ◽  
The Difference ◽  
Cohesive Energies ◽  
Heats Of Vaporization

The temperature dependence of heats of vaporization and some other derived thermodynamic properties were determined for four substituted hydrocarbons, viz. 2,2,4-trimethylpentane,1-octene, ethylbenzene and n-butylbenzene. The temperature dependence of heats of vaporization was measured and, on the basis of these data, the values of standard heats of vaporization, internal and cohesive energies, entropies of vaporization and the difference of heat capacities of liquid and vapour at constant pressure and along the saturated vapour pressure curve were computed.

scholarly journals Enthalpy Relaxation Phenomenon of Heavy Ice

1979 ◽  
Vol 22 (86) ◽  
pp. 155-164 ◽  
Author(s):  
Osamu Haida ◽  
Hiroshi Suga ◽  
Syūzō Seki
Keyword(s):  
Heat Capacity ◽  
Vapour Pressure ◽  
Activation Enthalpy ◽  
Thermal Anomaly ◽  
Adiabatic Calorimeter ◽  
Heat Capacity Data ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Relaxational Process ◽  
Capacity Data

AbstractThe heat capacities of quenched and annealed heavy ice Ih were measured in the temperature range 14 to 300 K by an adiabatic calorimeter. A relaxational thermal anomaly was found at around 115K and this phenomenon was ascribed to the onset of deuteron ordering in the crystal. The average activation enthalpy of the relaxational process was determined to be (26±5) kJ mol–1. Residual entropies of the crystal were recalculated on the basis of the present heat-capacity data combined with the revised values for enthalpy of vapourization, saturated vapour pressure, and spectroscopic entropy. They are (3.47±0.41) J K–1mol–1for the quenched crystal and (3.44±0.41) J K–1mol–1for the crystal annealed at 102–106 K for 264 h. The characteristics and the origin of the anomaly are discussed in comparison with that of ordinary ice.

scholarly journals Raoult’s law revisited: accurately predicting equilibrium relative humidity points for humidity control experiments

2016 ◽  
Author(s):  
Michael G. Bowler ◽  
David R. Bowler ◽  
Matthew W. Bowler
Keyword(s):  
Relative Humidity ◽  
Vapour Pressure ◽  
Control Device ◽  
Raoult’S Law ◽  
Simple Argument ◽  
Humidity Control ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Equilibrium Relative Humidity ◽  
Raoult's Law

AbstractThe humidity surrounding a sample is an important variable in scientific experiments. Biological samples in particular require not just a humid atmosphere but often a relative humidity (RH) that is in equilibrium with a stabilizing solution required to maintain the sample in the same state during measurements. The controlled dehydration of macromolecular crystals can lead to significant increases in crystal order, which often leads to higher diffraction quality. Devices that can accurately control the humidity surrounding crystals on a beamline have led to this technique being increasingly adopted, as experiments become easier and more reproducible. Matching the relative humidity to the mother liquor is the first step to allow the stable mounting of a crystal. In previous work, we measured the equilibrium relative humidity for a range of concentrations of the most commonly used precipitants and showed how this related to Raoult’s law for the equilibrium vapour pressure of water above a solution. However, a discrepancy between measured values and those predicted by theory could not be explained. Here, we have used a more precise humidity control device to determine equilibrium relative humidity points. The new results are in agreement with Raoult’s law. We also present a simple argument in statistical mechanics demonstrating that the saturated vapour pressure of a solvent is proportional to its mole fraction in an ideal solution: Raoult’s Law. The same argument can be extended to the case where solvent and solute molecules are of different size, as is the case with polymers. The results provide a framework for the correct maintenance of the RH surrounding samples.SynopsisThe equilibrium relative humidity values for a number of the most commonly used precipitants in biological macromolecule crystallisation have been measured using a new humidity control device. A simple argument in statistical mechanics demonstrates that the saturated vapour pressure of a solvent is proportional to its mole fraction in an ideal solution (Raoult’s Law). The same argument can be extended to the case where solvent and solute molecules are of different size.

scholarly journals Enthalpy Relaxation Phenomenon in a Heavy Ice Crystal

1978 ◽  
Vol 21 (85) ◽  
pp. 707
Author(s):  
Osamu Haida ◽  
Hiroshi Suga ◽  
Syūzō Seki
Keyword(s):  
Heat Capacity ◽  
Activation Enthalpy ◽  
Thermal Anomaly ◽  
Adiabatic Calorimeter ◽  
Enthalpy Of Vaporization ◽  
Ice Crystal ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Relaxational Process ◽  
Capacity Data

Abstract The heat capacities of quenched and annealed heavy ice Ih were measured in the temperature range 14 to 300 K by an adiabatic calorimeter. A relaxational thermal anomaly was found at around 115 K and this phenomenon was ascribed to the onset of deuteron ordering in the crystal. The average activation enthalpy of the relaxational process was determined to be (26±5) kJ mol-1. Residual entropies of the crystal were recalculated on the basis of the present heat-capacity data combined with the revised values for enthalpy of vaporization, saturated vapour pressure, and spectroscopic entropy. They are (3.47±0.41 J K-1 mol-1 for the quenched crystal and (3.44±0.41) J K-1 mol-1 for a crystal annealed at 102-106 K for 264 h. The characteristics and the origin of the anomaly are discussed in comparison with that of ordinary ice. This paper has been accepted for publication in full in a forthcoming issue of the Journal of Glaciology.

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