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CRITICAL CONSTANTS HELP

Allows the prediction through calculation of the critical constants of compounds. The method employs using Lydersen’s method.

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Download : chemcesd.zip  

ChemMathsInfo : Further Details  

The Equations used are :

Tc = Tb/[0.567 + ΔT- (ΔT)2]

Pc = M/(0.34 + ΔP)2

Vc = 0.04 + ΔV

Tc = critical temperature, k.

Pc = critical pressure, atm

Vc = molar volume at the critical conditions, m^3/kmol.

Tb = normal boiling point, k.

ΔT, ΔP, ΔV = critical temperature, pressure and molar volume increments. These are all calculated by the program, using Lydersen, 1955 data points.

Method of use :

The contribution values of the compound can be changed and the critical values re-calculated for.

Example diphenylmethane :

Group Number ΔT ΔP ΔV

C 10 0.11 1.54 0.37

= C –(ring) 2 0.022 0.308 0.072

--CH2-- 1 0.02 0.227 0.055

Totals: 0.152 2.075 0.497

Hence : Predicted Critical values via calculations are :

Tc = 772 k

Pc = 28.8 atm

Vc = 0.537 m3/Kmol