Chapter6a

# Chapter6a - Phase Diagram of 4He Examples 1 For S(Rhombic...

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Phase Diagram of 4 He

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1) For S(Rhombic) S(Monoclinic), at 298 K, r G° = 0.33 kJ. S m °(R) = 31.8 and S m °(M) = 32.6 JK -1 mol -1 . At what temperature will the two forms coexist at 1 bar? d( r G°)/dT = - r S° = - 0.8 J/K Integrating, r G°(T) - r G°(T 1 ) = - r S°(T - T 1 ) where T is the desired temperature. But r G°(T) = 0 (Why?) whence T = 710 K Examples:
2) For water at 0ºC, fus Η = 6.008 kJ/mole, the densities of ice and liquid water are 0.91671 and 0.99984 g/cm 3 respectively. Estimate the pressure required to lower the melting point by 1ºC. dp/dT = fus Η /T fus V = - 1.35x10 7 Pa/K Assuming this to be constant, p - 1.013x10 5 = - 1.35x10 7 (T - 273.15) is the equation of the melting line. For T =272.15 K, P = 1.36x10 7 Pa = 134 bar.

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4) Estimate the normal boiling point of benzene given that its vapour pressure is 20.0 kPa at 35.0 ºC and 50.0 kPa at 58.8 ºC. ln (p 2 /p 1 ) = - ( vap H/R)(1/T 2 - 1/T 1 ) Using the data given, find vap H = 32.8 kJ/mole. Applying the equation again with one of the values of the pressure being 1 atm = 101.3 kPa, find the normal boiling temperature to be 353 K 80 ºC.
Thermodynamics of Solutions

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Solvent: Major Component Solute: Minor Component Mole Fraction of constituent i, x i = n i /(n 1 + n 2 + n 3 +····) = n i / Σ n i Clearly, Σ x i = 1. Molality ‘m’ is the number of moles of solute per kilogram (unit mass) of solvent. Molarity
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Chapter6a - Phase Diagram of 4He Examples 1 For S(Rhombic...

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