The critical properties, critical temperature , critical pressure , and critical volume , and the acentric factor are required by the liquid multi-phase Chemkin application, they are used by the curve-fitting equations for liquid species property evaluation and by the mixing rules for mixture critical property estimation.

The critical properties of a liquid species should be given in the LIQPROP thermodynamic block of the surface mechanism input file. The format of the critical properties is described in Table 2.3: Required liquid species properties.

The liquid standard-state enthalpy is the species enthalpy in the liquid state at the standard condition ( = 298.15K and = 1 atm) and is used as the reference value to compute the liquid enthalpy of the species at different temperatures. If the liquid standard-state enthalpy cannot be found for a species, Chemkin can estimate it from the gas-phase standard-state enthalpy, heat of vaporization, and the enthalpy departure function computed by the SRK cubic equation of state. The liquid standard-state enthalpy obtained by this method is usually in good agreement with the measured value.

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The format of the standard-state enthalpy input is given in Table 2.3: Required liquid species properties.

The liquid standard-state entropy is the species entropy in the liquid state at the standard condition and is used as the reference value to compute the liquid entropy of the species at different temperatures. If the liquid standard-state enthalpy cannot be found for a species,Chemkin can estimate it from the gas-phase standard-state entropy, heat of vaporization, and the entropy departure function computed by the SRK cubic equation of state. The liquid standard-state enthalpy obtained by this method does show relatively large discrepancy against the measured value.

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The format of the standard-state enthalpy input is also provided in Table 2.3: Required liquid species properties below:

Table 2.3: Required liquid species properties

Property Name	Syntax	Units
Critical Properties	criticalproperties=	critical pressure [bar], critical temperature [k], critical volume [cm3]
Acentric factor	acentricfac=	acentric factor [-]
Liquid Std. Enthalpy	refliqenthalpy=	reference liquid-state enthalpy at 298.15 K [J/mol]
Gas Std. Enthalpy	refvapenthalpy=	reference gas-phase enthalpy at 298.15 K [J/mol]
Liquid Std. Entropy	refliqentropy=	reference liquid-state entropy at 298.15 K [J/mol-K]
Gas Std. Entropy	refvapentropy=	reference gas-phase entropy at 298.15 K [J/mol-K]
Gas Thermodynamic Data	refvaptherm=	Gas-phase thermodynamic data in NASA7 () or NASA9 () format

The heat of vaporization is usually given as a function of temperature. It is not directly used by the liquid multi-phase application but is used by several sub-models to evaluate other liquid properties. The heat of vaporization is a required data and must be provided in the LIQPROP block. The available models and the input formats are given in Table 2.4: Heat of Vaporization models in Chemkin below:

Table 2.4: Heat of Vaporization models in Chemkin

Model Name (units)	Syntax	Equation Form
DIPPR106 (J/kmol)	heatvaporization=(DIPPR106) a b c d e
Constant (J/mol)	heatvaporization=(CONSTANT)

The vapor pressure is usually given as a function of temperature. It is not directly used by the liquid multi-phase application but is used by several sub-models to evaluate boiling temperature and liquid mixture properties. The vapor pressure is a required data and must be included in the LIQPROP block. The available models and the input formats are given in Table 2.5: Vapor Pressure model in Chemkin below:

Table 2.5: Vapor Pressure model in Chemkin

Model Name (units)	Syntax	Equation Form
DIPPR101 (Pa)	vaporpressure=(DIPPR101) a b c d e
DIPPR115(Pa)	vaporpressure=(DIPPR115) a b c d e
Antoine-NIST (bar)	vaporpressure=(ANTOINE) a b c
Constant (Pa)	vaporpressure=(CONSTANT)