Enthalpies of Fusion and Transition of Organic Compounds

461 Pages·1995·1.448 MB·English

by  K. N. Marsh (eds.)

Landolt-Börnstein
Numerical Data and Functional Relationships in Science and Technology
New Series / Editor in Chief: W. Martienssen
Group IV: Macroscopic Properties of Matter
Volume 8
Thermodynamic Properties
of Organic Compounds
and their Mixtures
Subvolume A
Enthalpies of Fusion and Transition
of Organic Compounds
Z.-Y. Zhang, M. Frenkel, K.N. Marsh, R.C. Wilhoit
Edited by K.N. Marsh
Editor
K.N. Marsh
Thermodynamics Research Center
The Texas A&M University System
College Station, Texas 77843-3111, USA
Authors
Z.-Y. Zhang
M. Frenkel
K.N. Marsh
R.C. Wilhoit
Thermodynamics Research Center
The Texas A&M University System
College Station, Texas 77843-3111, USA
Landolt-Börnstein / New Series
Berlin
Heidelberg
New York
Barcelona
Budapest
Hong Kong
London
Milan
Paris
Tokyo
Preface
Experimental data on the enthalpies of solid–solid and solid–liquid transitions for organic compounds
is critically important from both a scientific and practical point of view. A knowledge of these properties
is necessary to calculate energy balances for solid and liquid transfers and transitions during production
processes in the chemical and related industries. Other industrial applications of these data include their
application in liquid crystals in electronics and the development of reference materials to calibrate
commercially manufactured testing equipment such as differential scanning calorimeters used for the
determination of the temperature and amount of energy produced or consumed during phase changes.
From a theoretical perspective, these data represent ‘working material’ that can be used to develop
methods for the prediction of thermodynamic properties of organic compounds in the liquid and solid
states based on their structural attributes. Another field of the use of these data is the calculation of the
solubilities of organic compounds based on temperature and enthalpy of fusion information. These
considerations influenced the authors to prepare a comprehensive critical evaluation of all known
thermodynamic data on solid–solid and solid–liquid phase transitions for organic compounds.
Enthalpies of solid–solid and solid–liquid transitions have been partially compiled in the monographs
by Domalski, Evans and Hearing [84-dom/eva, 90-dom/hea]. Because the primary focus of that
compilation was on heat capacities and entropies, the authors emphasized that no specific search for the
enthalpies of phase transitions was made and the data they reported were obtained as a by-product of their
heat capacity search. Further, the data published in Domalski et al. [84-dom/eva] and Domalski and
Hearing [90-dom/hea] covered the original literature only up to 1989.
Two compilations on the enthalpies of fusion of organic compounds have been prepared by Acree [91-
acr, 93-acr] and some old information on the enthalpies of the phase transitions have been compiled in
International Critical Tables [29-ano] and in earlier Landolt-Börnstein Tables [23-ano, 55-ano]. A
common drawback of the compilations discussed above is the absence of a detailed evaluation of the
quality and accuracy of the data. Further, the compilations do not provide recommended values for
thermodynamic properties of the phase transition. An evaluation to provide recommended values is not an
easy task because of different methods used for the experimental determination of the properties, different
quality of the samples used, reproducibility etc. An evaluation to provide recommended values for the
thermodynamic properties of the phase transitions often requires the assessment of the quality of five to
ten independent values reported for the same phase transition, where in some cases these values differ by a
factor of two.
In the present volume IV/8A, the temperatures and the enthalpies of both solid–solid and solid–liquid
phase transitions were collected from the original literature published from the end of last century to early
1995. All the values, including those from the five references listed below, were critically evaluated to
provide recommended values in the cases where several experimental values were reported for the same
phase transition. The accuracies of both the original and recommended values were determined and
information was given regarding the sample purity and method of measurement.
As a result of our search, data for 2441 compounds (a total of 3682 solid–solid and solid–liquid
transitions including phase transitions of liquid and plastic crystals) were compiled and evaluated. The
values were taken from 1059 publications. Phase transitions of polymers were not considered.
This volume consists of three chapters; a list of the references, and two indexes (Chemical Abstract
Service Registry Number Index and Chemical Name Index). Chapter 1 describes the basic concepts of
enthalpy of transition and fusion including their classification, temperature dependence, and applications.
Chapter 2 is a brief review of the experimental methods used to determine the enthalpies of transition and
fusion including both direct and indirect methods. Chapter 3 contains the tabulated original and evaluated
values and auxiliary information including how these values were collected and evaluated (scope of the
search, selection of the experimental data, and recommended data evaluation).
This volume will be useful to a wide community of researchers, specialists, and engineers working in
the fields of physical and organic chemistry, chemical engineering, electronics, material science, chemical
aspects of energy technology, and those developing computerized predictive packages. The book should
also be of use to students and faculty in Chemistry and Chemical Engineering Departments at universities
as a reference book for courses in Advanced Physical Chemistry and Thermodynamics.
Acknowledgments
The authors wish to express their sincere appreciation to staff members of the Thermodynamics
Research Center (TRC), A Division of the Texas Engineering Experiment Station, at The Texas A&M
University System. Our special thanks to Sheila Fenelon who has prepared a camera-ready copy of the
manuscript in Word for Windows 6.0. Also we would like to thank Mark Sutton for the search of
Chemical Abstract Registry Numbers of the compounds selected and Atri Das for extensive work related
to entering and checking the literature references.
College Station, Texas, June 1995 Z.-Y. Zhang, M. Frenkel, K.N. Marsh, R.C. Wilhoit
References
23-ano Landolt-Börnstein, Physikalisch-Chemische Tabellen, Fünfte umgearbeitete Auflage,
Zweiter Band: Schmelzwärme Organischer Verbindungen. Walter A. Roth und Karl
Scheel (eds.), Berlin: Springer-Verlag, 1923, p. 1471-4.
29-ano International Critical Tables of Numerical Data: Physics, Chemistry and Technology.
Volume 5, New York: McGraw-Hill, 1929.
55-ano Landolt-Börnstein, Zahlenwerte und Funktionen, Sechste Auflage, II. Band:
Eigenschaften der Materie in ihren Aggregatzuständen.4. Teil: Kalorische
Zustandsgrößen, Organische und anorganisch-organische Verbindungen. Berlin:
Springer-Verlag, 1955, p. 261.
84-dom/eva Domalski, E. S.; Evans, W. H.; Hearing E. D.: Heat Capacities and Entropies of
Organic Compounds in the Condensed Phase.
J. Phys. Chem. Ref. Data 13 (1984) Supplement No 1.
90-dom/hea Domalski, E. S.; Hearing E. D.: J. Phys. Chem. Ref. Data 19 (1990) 881.
91-acr Acree, W. E.: Thermochimica Acta 189 (1991) 37.
93-acr Acree, W. E.: Thermochimica Acta 219 (1993) 97.
1.1 Definitions 1
1 Basic Concepts of Enthalpies of Fusion and Transition
1.1 Definitions
anisotropic phase A phase in which properties associated with a particular direction in space,
such as refractive index, dielectric constant, thermal conductivity, or thermal
expansion, are different along different directions.
cholesteric liquid crystal A phase formed by chiral molecules which is similar to a nematic phase. The
molecules form helices whose axes are aligned along a particular direction.
crystal phase A phase which takes a fixed volume at a particular temperature and pressure
and whose shape remains unchanged unless subjected to large stresses. The
molecules in a crystal are confined to fixed positions in space that are
determined by a regular pattern. Crystals may be either isotropic or anisotropic.
cryoscopic constant The constant of proportionality between the mole fraction (or molality) of a
solute and the depression of the freezing point, see equation (1.9).
discotic liquid crystal A liquid crystal formed from disc-shaped molecules. The molecules are stacked
in parallel columns. Several subtypes have been identified.
enantiotropic phase A phase that is metastable at all temperatures and pressures.
enthalpy of fusion The enthalpy change for the transition from a crystal phase to a liquid phase.
entropy of fusion The entropy change for the transition from crystal phase to a liquid phase.
enthalpy of transition The difference in enthalpy between two phases. It is taken in the direction that
gives a positive value. It is usually applied to two phases at equilibrium at the
same temperature and pressure. It may, however, be applied to a monotropic
transition.
entropy of transition The difference in entropy between two phases. It is taken in the direction that
gives a positive value. It is usually applied to two phases at equilibrium at the
same temperature and pressure. It may, however, be applied to a monotropic
transition.
eutectic temperature The temperature of equilibrium between a liquid mixture and the crystal phases
of each component.
first order transition A transition between two phases at the same temperature and pressure in which
the chemical potentials of each component is the same in both phases, but
temperature and pressure derivatives of the chemical potentials, such as
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2 1.1 Definitions
entropy, volume, and heat capacity are discontinuous.
freezing point The temperature of first appearance of a solid phase when cooling a liquid in
equilibrium with air at one atmosphere. For a single component system, the
freezing point is the same as the melting point.
glass phase An isotropic phase in which molecules are confined to small translational
motions but do not exhibit long range order. Glasses typically have very high
viscosities and, in this respect, resemble crystals.
glass transition A relatively narrow range of temperature in which a liquid changes to a glass. It
is often regarded as a second order transition. The temperatures associated with
a glass transition are somewhat dependent on the method of observation.
heat of fusion The heat absorbed for the transition of a crystal to a liquid phase at a fixed
temperature and pressure. Same as the enthalpy of fusion.
heat of transition The heat absorbed for the transition of one phase to another at fixed
temperature and pressure. Same as the enthalpy of transition.
isotropic phase A phase in which properties associated with a direction in space, such as
refractive index, dielectric constant, thermal conductivity, or thermal
expansion, are the same for all directions.
irreversible transition A transition between two states not at equilibrium. At a fixed temperature and
pressure the direction of change is toward the state with the lowest (most
negative) Gibbs energy. The direction of change can not be reversed by small
changes in the imposed conditions.
lambda transition A second or higher order transition.
latent heat of fusion See enthalpy of fusion.
liquid crystal A liquid phase characterized by some degree of long range molecular order.
(See cholesteric, nemactic, smectic and discotic liquid crystals.) Liquid crystals
are usually anisotropic but, in principle, may be isotropic.
liquid phase An isotropic phase characterized by fluid flow, which has a fixed volume at a
particular temperature and pressure but whose shape is determined by the
container. The molecules in a liquid are not confined to fixed positions and do
not exhibit long range order.
melting point The temperature of first appearance of a liquid phase when heating a solid in
equilibrium with air at one atmosphere. The melting point of a single
component system is the same as the freezing point.
mesogens Substances that form liquid crystal phases.
mesomorphic transition A phase transition in which at least one phase is a liquid crystal.
mesophases Liquid crystal phases.
metastable phase A phase that is not the stable phase at a particular temperature and pressure.
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1.1 Definitions 3
Such phases may physically exist but potentially will spontaneously transform
to the stable phase. A metastable liquid is often called undercooled.
monotropic phases Two or more crystalline phases for a system in which each is stable over a
particular range of temperature. A monotropic phase is metastable outside its
range of stability.
monotropic transition See irreversible transition.
nematic liquid crystal A liquid crystal in which the long axes of the molecules are statistically aligned
along a particular direction in space. The centers of gravity of the molecules are
disordered.
n-th order transition A transition between two phases at the same temperature and pressure in which
the chemical potentials, and all temperature derivatives through the (n-1)th are
continuous, but the n-th is discontinuous.
phase An portion of a material system which is uniform in chemical composition and
in intensive physical properties.
phase transition A change in the nature of a phase or in the number of phases as a result of some
variation in imposed conditions such as temperature, pressure, or chemical
potential of a component.
plastic crystal A crystal phase in which the molecules have some degree of rotational
freedom.
polymorphism The existence of more than one crystalline phase for a system.
reversible transition A change from one state to another at mutual equilibrium. The direction of
change may be reversed by an infinitesimal change in imposed conditions such
as temperature of pressure. (See also first order transition.)
saturated phase A crystal or liquid phase that is in equilibrium with the gas phase.
smectic liquid crystals Liquid crystals in which the molecules have an orientational long range order
and also some type of laminar order. There are several types of smectic phases
which correspond to various kinds of ordering.
stable phase The thermodynamically stable phase at a particular temperature and pressure.
Its chemical potential is lower (more negative) than all other phases.
thermotropic liquid crystals Two or more liquid crystal phases that exist in different temperature ranges.
triple point The temperature and pressure at which three phases of a single component
system exist in mutual equilibrium. This occurs at only a particular temperature
and pressure for three particular phases.
triple point pressure The pressure at the triple point for three particular phases in equilibrium.
triple point temperature The temperature at the triple point for three particular phases in equilibrium.
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4 1.2 Thermodynamic Principles of Phase Transitions
undercooled liquid A liquid below its freezing point. It is metastable at this temperature.
1.2 Thermodynamic Principles of Phase Transitions
Two phases at the same temperature and pressure are in mutual equilibrium when the chemical
potentials of each of the components are the same in the both phases. Under these conditions material
from one phase can be reversibly converted to the other by the addition or removal of energy in the form
of heat. The intensive thermodynamic properties of a system consisting of a single component and a
single phase are functions of two independent variables. The choice of independent variables is arbitrary
but temperature and pressure are a common choice. A system of C components and P independent phases
has P(C + 1) variables. Equilibrium among the phases introduces (C + 2)(P - 1) constraints. The net
number of independent variables is then F = C - P + 1, which is the well-known Gibbs phase rule.
In a one component system the chemical potential is the same as the Gibbs energy per mole. In this
case two phases at equilibrium at the same temperature and pressure have the same Gibbs energy per
mole. Figure 1.1 illustrates the Gibbs energy per mole for three phases for a one component system as a
function of temperature at constant pressure.
The crossing points correspond to the temperature of equilibrium between two phases at this pressure.
The slopes of the Gibbs energy lines are given by,
∂ G
  =−S (1.1)
∂ T
p
In first order transitions, the slopes are discontinuous at the equilibrium temperature. The discontinuity equals
the difference of entropy of the two phases.
The rate of change of the temperature of equilibrium between two phases with change in pressure is
given by the Clausius-Clapyeron equation,
dT T ∆ V
= trs (1.2)
dP ∆ H
trs
The enthalpy of transition from the low temperature phase to the high temperature phase is positive. For
condensed phases the corresponding change in volume, ∆ V, is usually positive but may be negative in some
trs
instances. The normal range of values for organic compounds shows that the transition temperature changes in
the range of about -0.01 to 0.02 K⋅MPa-1.
When a system changes state at constant temperature and pressure in a manner that only p - V work is
done, the process is spontaneous when there is a decrease in the Gibbs energy. Thus the state having the
lowest (most negative) Gibbs energy is the final equilibrium state of the system at a particular
temperature and pressure. Thus in Figure 1.1 the phase having the lowest Gibbs energy at any particular
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