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Unformatted text preview: 1 Chemistry 260 Lecture 29 November 14, 2011 1 Today in Chemistry 260 Finish phase transitions Mixtures and their properties Measures of concentration Partial molar properties Spontaneous mixing Ideal solutions Real solutions Colligative properties 2 Striking Example Boiling by freezing http://www.youtube.com/watch? v=8oCjj8iDB9I Definitions: molar concentration ) ( ] [ 1 M L mol V n solution of volume solute of amount J J = = = molality b J = moles of solute mass of solvent = n J m solvent ( mol kg 1 = m ) mole fraction x J = moles of solute total amount of molecules = n J n solvent : mixture component in excess; solute : other component Measures of Concentration 6 2 Binary mixture: V = n A V A + n B V B pure water pure ethanol V ethanol smaller V ethanol Components in mixtures have altered properties partial molar volume : volume occupied by a mole of solute or solvent in a mixture Partial Molar Volume 7 Volume occupied by one mole of a component: V i V = n A V A + n B V B + n C V C + ... Accounts for non-ideality The whole is not equal to the sum of its parts x i intermolecular interactions can change significantly in solution Partial Molar Volume 8 partial molar Gibbs energy : contribution of substance to the total Gibbs energy of the mixture G = G A + G B partial molar Gibbs energies also vary with composition! chemical potentials : measure of the ability of a component to bring about physical or chemical change G = n A A + n B B ( ) ( ) ln f i p f m m f m i m i p p G G p G p V d p n R T p = = = for an ideal gas: and p f = p; p i = p O : expressing changes with respect to the standard state O (1 bar) O ( ) ln m m p G p G nRT p = + O J J J p RT ln + = O Partial Molar Gibbs Energies: Chemical Potential 9 Chemical Potential Partial molar Gibbs energy G i = i G = n 1 1 + n 2 2 dG mix = i mixed dn i i separated dn i = i mixed i separated ( ) dn i Molar Gibbs energy for the ith component...
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- Fall '08