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Published byBennett Cooper Modified over 8 years ago
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Chem 300 - Ch 24/#3 Today’s To Do List Critical behavior in L-L solutions Activity Excess Thermo Functions
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T-x/y Plot
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NonIdeal Solns Azeotropes
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Extremes in Positive Deviations from RL: 2 Liquid Phases
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The Lever Rule: l Consider 2 phases (‘ & “) each containing 2 components (1 & 2) in equilibrium: l Let n’ tot = n’ 1 + n’ 2 etc l n’ tot /n” tot =(x” 2 – x 2 )/(x 2 – x’ 2 ) = (length)’’/(length)’
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C 6 H 12 /Nitrobenzene T-x 2-Phase Diagram
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H 2 O/Triethylamine T-x with Lower Critical Point
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H 2 O/Nicotine with upper & lower Critical T
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Activity: Measure of Soln Nonideality l dG = -SdT + VdP l 2 phases at const T and equilibrium dG T = VdP j soln = j vap j soln = j vap = j o (T) +RT ln P j l If soln is ideal (RL holds): P j = P* j x j j soln = j o (T) + RT ln P* j x j = j o (T) + RT ln P* j + RT ln x j j soln = j o (T) + j *(T) + RT ln x j
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Continued For nonideal solutions: P j = P* j a j where a j = j x j = activity of j at x j relative to RL j soln = j o (T) + j *(T) + RT ln a j l Comparing equations: a j = P real /P * a j /x i = j = P real /P * x i = P real /P ideal
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Measure γ & Activity (a)
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Activities relative to (a) R L & (b) H L
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Excess Functions G ID mix = RT(n 1 ln x 1 + n 2 ln x 2 ) l For nonideal soln mixing: G NID mix = RT(n 1 ln a 1 + n 2 ln a 2 ) G NID mix = RT(n 1 ln x 1 + n 2 ln x 2 +n 1 ln 1 + n 2 ln 2 ) G E = G NID mix - G ID mix = RT(+n 1 ln 1 + n 2 ln 2 )
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Calculated R for CS 2 /DMM Solns @ 35.2 ºC
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G E -x for CS 2 /DMM Solns
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Solution with T uc < T bp that shows Azeotrope
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Next Time Start Chapter 25: Solid-Liquid Solutions Solute?…Solvent?… Molarity?…Molality?… Colligative Properties
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