ASTM E2071-21

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2071 − 00 (Reapproved 2015) E2071 − 21
Standard Practice for
Calculating Heat of Vaporization or Sublimation from Vapor
Pressure Data
This standard is issued under the fixed designation E2071; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice describes the calculation of the heat of vaporization of a liquid or the heat of sublimation of a solid from
measured vapor pressure data. It is applicable to pure liquids, azeotropes, pure solids, and homogenous solid solutions over the
temperature range for which the vapor pressure equation fitted to the measured data is applicable.
NOTE 1—This practice is generally not applicable to liquid mixtures. For a pure liquid or azeotrope, composition does not change upon vaporization so
that the integral heat of vaporization is identical to the differential heat of vaporization. Non-azeotropic liquid mixtures change composition upon
vaporizing. Heat of vaporization data computed from this practice for a liquid mixture are valid only as an approximation to the mixture differential heat
of vaporization; it is not a valid approximation to the mixture integral heat of vaporization.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 There is no ISO standard equivalent to this practice.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D2879 Test Method for Vapor Pressure-Temperature Relationship and Initial Decomposition Temperature of Liquids by
Isoteniscope
E1142 Terminology Relating to Thermophysical Properties
E1194 Test Method for Vapor Pressure
E1719 Test Method for Vapor Pressure of Liquids by Ebulliometry
E1782 Test Method for Determining Vapor Pressure by Thermal Analysis
This practice is under the jurisdiction of Committee E37 on Thermal Measurements and is the direct responsibility of Subcommittee E37.10 on Fundamental, Statistical
and Mechanical Properties.
Current edition approved May 1, 2015March 1, 2021. Published May 2015April 2021. Originally approved in 2000. Last previous edition approved in 20102015 as
E2071 – 00 (2010).(2015). DOI: 510.1520/E2071-00R15.510.1520/E2071-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2071 − 21
3. Terminology
3.1 Symbols:
3.1.1 A, B, C—Antoine vapor pressure equation constants (log , kPa, K), Antoine vapor pressure equation:
log P 5 A 2 B/ T1C (1)
~ !
3.1.2 P—vapor pressure, kPa.
3.1.3 P —critical pressure, kPa.
c
3.1.4 P —reduced pressure = P/P .
r c
3.1.5 T—absolute temperature, K.
3.1.6 T —critical temperature, K.
c
3.1.7 T —reduced temperature = T/T .
r c
3.1.8 V—molar volume, cm /mol.
3.1.9 R—gas constant, 8.31433 J/mol-K; 8314330 kPa-cm /mol-K.
3.1.10 ΔH —heat of vaporization, J/mol.
V
3.1.11 ΔZ —difference in compressibility factor (Z = PV/RT) upon vaporization. Clapeyron equation:
V
ΔH 52RΔZ d lnP /d 1/T (2)
@ ~ ! ~ !#
V V
ΔH 52RΔZ d lnP /d 1/T (2)
@ ~ ! ~ !#
V V
3.1.11.1 Discussion—
The subscript “V” will be used throughout this practice to designate the vaporization of a liquid. If the vapor pressure data were
measured for a solid, substitute the subscript “S” for the sublimation of a solid.
3.2 Definitions:Definitions
3.2.1 Specialized terms used in this practice are defined in Terminology E1142.—Specialized terms used in this practice are
defined in Terminology E1142.
3.2.1 sublimation—transition from a solid phase to a gaseous phase.
3.2.2 vaporization—transition from a liquid phase to a gaseous phase.
4. Summary of Practice
4.1 Vapor pressure data are measured by other referenced ASTM standards and then correlated with the Antoine equation. The heat
of vaporization or sublimation is computed at the desired temperature from the vapor-pressure temperature derivative from the
fitted Antoine equation by use of the Clapeyron equation (1). In the Clapeyron equation, ΔZ is determined by either the
V
Clausius-Clapeyron (21) approximation:
~ΔZ 5 1!
V
or the Haggenmacher (32) approximation:approximations.
ΔZ 5 12 P /~T !
S $ @ #% D
V r r
4.2 An example calculation is given in Annex A1.
The boldface numbers given in parentheses refer to a list of references at the end of the text.this standard.
E2071 − 21
5. Significance and Use
5.1 If the heat of vaporization or sublimation is absorbed or liberated in a process at constant pressure, it is called enthalpy of
vaporization or sublimation. Enthalpy of vaporization or sublimation is a fundamental thermodynamic property of a liquid or solid.
It is an important quantity in the design of heat exchangers and other chemical process units. Enthalpy of vaporization is also used
to calculate solubility parameters (43).
5.2 This practice may be used in research, regulatory compliance, and quality assurance applications.
6. Experimental Vapor Pressure Data
6.1 Vapor pressure data are measured by Test Methods D2879, E1194, E1719, or E1782. Note the safety precautions contained
in the test method used.
6.1.1 Vapor pressure data from other reliable sources, for example, peer-review technical journals, may be used. The source of the
vapor pressure data must be noted.
6.2 The measured vapor pressure data are fitted to an Antoine vapor pressure equation. See 10.3 in Test Method E1719 for details
on least-squares regression of vapor pressure data.
7. Calculation
7.1 At each temperature of interest, calculate the vapor pressure from the Antoine equation and calculate the vapor-pressure
temperature derivative from the fitted Antoine equation constants from:
2 2
d lnP /d 1/T 522.3025851 BT / T1C (3)
@ ~ ! ~ !# @ ~ ! #
2 2
@d~lnP!/d~1/T!# 522.3025851@BT /~T1C! # (3)
7.2 Calculate an approximation to ΔZ at each temperature.
V
7.2.1 The Clausius-Clapeyron approximation to Δ Z is:
V
ΔZ [1.0 (4)
V
7.2.2 The Haggenmacher approximation to ΔZ is:
V
ΔZ 5 12 P / T 2 (5)
$ @ ~ ! #%
V r r
NOTE 2—The Clausius-Clapyeron approximation is generally used for solids and for liquids at low T . The Haggenmacher approximation is generally used
r
for liquids up to T ≈ 0.75.
r
7.2.3 If equation of state (Z) data are available for both the condensed and gaseous phases, ΔZ may be calculated directly from
V
the equation of state data.
7.3 Calculate the heat of vaporization or heat of sublimation at each temperature from the Clapeyron equation:
ΔH 52RΔZ d lnP /d 1/T (6)
@ ~ ! ~ !#
V V
ΔH 52RΔZ @d~lnP!/d~1/T!# (6)
V V
8. Report
8.1 Report the following information:
8.1.1 The test method and source of the vapor pressure data used in the heat of vaporization or heat of sublimation calculation.
A vapor pressure data table shall a
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