ASTM_E_2071_-_00_2015.pdf

Designation:E207100(Reapproved 2015)Standard Practice forCalculating Heat of Vaporization or Sublimation from VaporPressure Data1This standard is issued under the fixed designation E2071;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice describes the calculation of the heat ofvaporization of a liquid or the heat of sublimation of a solidfrom measured vapor pressure data.It is applicable to pureliquids,azeotropes,pure solids,and homogenous solid solu-tions over the temperature range for which the vapor pressureequation fitted to the measured data is applicable.NOTE1This practice is generally not applicable to liquid mixtures.For a pure liquid or azeotrope,composition does not change uponvaporization so that the integral heat of vaporization is identical to thedifferential heat of vaporization.Non-azeotropic liquid mixtures changecomposition upon vaporizing.Heat of vaporization data computed fromthis practice for a liquid mixture are valid only as an approximation to themixture differential heat of vaporization;it is not a valid approximation tothe mixture integral heat of vaporization.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.3 There is no ISO standard equivalent to this practice.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D2879 Test Method for Vapor Pressure-Temperature Rela-tionship and Initial Decomposition Temperature of Liq-uids by IsoteniscopeE1142 Terminology Relating to Thermophysical PropertiesE1194 Test Method for Vapor Pressure(Withdrawn 2013)3E1719 Test Method for Vapor Pressure of Liquids by Ebul-liometryE1782 Test Method for Determining Vapor Pressure byThermal Analysis3.Terminology3.1 Symbols:3.1.1 A,B,CAntoine vapor pressure equation constants(log10,kPa,K),Antoine vapor pressure equation:log10P 5 A 2 B/T1C!3.1.2 Pvapor pressure,kPa.3.1.3 Pccritical pressure,kPa.3.1.4 Prreduced pressure=P/Pc.3.1.5 Tabsolute temperature,K.3.1.6 Tccritical temperature,K.3.1.7 Trreduced temperature=T/Tc.3.1.8 Vmolar volume,cm3/mol.3.1.9 Rgas constant,8.31433 J/mol-K;8314330 kPa-cm3/mol-K.3.1.10 HVheat of vaporization,J/mol.3.1.11 ZVdifference in compressibility factor(Z=PV/RT)upon vaporization.Clapeyron equation:HV5 2RZVdlnP!/d1/T!#3.1.11.1 DiscussionThe subscript“V”will be usedthroughout this practice to designate the vaporization of aliquid.If the vapor pressure data were measured for a solid,substitute the subscript“S”for the sublimation of a solid.3.2 Definitions:3.2.1 Specialized terms used in this practice are defined inTerminology E1142.3.2.2 sublimationtransition from a solid phase to a gas-eous phase.3.2.3 vaporizationtransition from a liquid phase to agaseous phase.1This practice is under the jurisdiction of Committee E37 on Thermal Measure-ments and is the direct responsibility of Subcommittee E37.10 on Fundamental,Statistical and Mechanical Properties.Current edition approved May 1,2015.Published May 2015.Originallyapproved in 2000.Last previous edition approved in 2010 as E2071 00(2010).DOI:510.1520/E2071-00R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.Summary of Practice4.1 Vapor pressure data are measured by other referencedASTM standards and then correlated with the Antoine equa-tion.The heat of vaporization or sublimation is computed at thedesired temperature from the vapor-pressure temperature de-rivative from the fitted Antoine equation by use of theClapeyron equation(1).4In the Clapeyron equation,ZVisdetermined by either the Clausius-Clapeyron(2)approxima-tion:ZV5 1!or the Haggenmacher(3)approximation:SZV5$1 2Pr/Tr!3#%12D4.2 An example calculation is given in Annex A1.5.Significance and Use5.1 If the heat of vaporization or sublimation is absorbed orliberated in a process at constant pressure,it is called enthalpyof vaporization or sublimation.Enthalpy of vaporization orsublimation is a fundamental thermodynamic property of aliquid or solid.It is an important quantity in the design of heatexchangers and other chemical process units.Enthalpy ofvaporization is also used to calculate solubility pa