页数：52页文件大小：2.98 MB来源： Atkins’PhysChem物理化学ppt课件
本课件系统讲混合物：从液体的化学势出发给出拉乌尔定律与理想溶液模型，讨论溶剂与溶质的活度、亨利定律与标准态选择，最后给出稀溶液的依数性——蒸气压降低、沸点升高、凝固点降低与渗透压。
Partial Molar quantities G = n A μ A + n B μ B
p A = xApA * p B = xBKB
The Properties of Solutions Liquid Mixtures Colligative Properties （依数性） Activities
7.4 Liquid Mixtures (a) Ideal Solutions Gibbs energy of mixing for two liquids is calculated the same a
(a) Ideal Solutions Liquid Mixtures: Miscibility Solution ideality is quite different from perfect gas
(a) Ideal Solutions Liquid Mixtures: Miscibility Sometimes, molecules of one type might cluster togethe
(b) Excess function and regular Solutions Thermodynamic properties of real solutions are described with excess functions, XEF
(b) Excess function and regular Solutions Deviations of the excess energies from zero indicates the degree to which a solutio
(b) Excess function and regular Solutions (a) The benzene / cyclohexane mixing, shows that mixing is endothermic. (b) Tetrach
(b) Excess function and regular Solutions Discuss in more quantitative Suppose the excess enthalpy depends on composition: HE
(b) Excess function and regular Solutions For regular solution, the entropy of mixing has its ideal value. SE = 0 the nGE = H
7.5 Colligative properties Colligative properties literally denotes properties which depend on a collection of
(a) The common features of colligative properties All colligative properties result from lowering of the chemical potential of the so
(a) The common features of colligative properties What causes the lowering of chemical potential of a liquid? Not the energies of int
Solvents, Solutes and Entropy There is no direct effect of the solute on the chemical potential of the solvent va
Solvents, Solutes and Entropy (a) Solution with entropy S & p A *, vapour pressure reflects tendency to greater S
(b) The elevation of boiling point Heterogeneous eqm: between solvent in solution and solvent vapour at 1 at m, where
(b) The elevation of boiling point Justification of eqn Δ T = KxBWhenxB = 0, T = T * When x B = < < 1, ln (1 - x B) =
(b) The elevation of boiling point In Δ T = KxB, the identity of solute is irrelevant: just the mole fraction is impor
(c) The depression of freezing point Heterogeneous eqm: pure solid solvent A and solution with solute present in mole fr
(c) The depression of freezing point If solution is dilute, x B b (molality, molkg - 1), in dilute solutions Larger de
(d) Solubility If solid and liquid are in contact, solid dissolves until the solution is saturated
(d) Solubility At melting point, T *, Δ fusG = 0 What mole fraction of B is in solution at T?
(d) Solubility Solubility of B decreases exponentially as the temperature is decreased, T * is m.
(e) Osmosis There are many times in nature when a solvent will pass spontaneously through a sem
(e) Osmosis Eqm is established when the hydrostatic pressure of the solution in the column is e
(e) Osmosis To treat osmosis thermo chemically, we note that at equilibrium, chemical potential
(e) Osmosis Pure solvent side: µ A * (p) at p, Solution side: x A < 1, so µ A * is lowered by s
(e) Osmosis Take pressure into account: Combining equations, we have For dilute solutions: lnxA
(e) Osmosis One of the most important examples is the transport of fluids through living cell m
(e) Osmometry Osmotic pressure is easily measured, and is quite large. Osmometry can be applied f
(e) Osmometry Osmotic pressure is measured at various concentrations, c, and plotting Π / c again
(e) Osmometry c (g L - 1) 1.00 2.00 4.00 7.00 9.00 h (cm) 0.28 0.71 2.01 5.10 8.00 With [B] = c /
(e) Osmometry Therefore, to find M, plot h / c against c, and except a straight line with interce
(e) Osmometry C (g L - 1) 1.00 2.00 4.00 7.00 9.00 h / c (cm) 0.28 0.36 0.53 0.729 0.889 The data
(f) Vapour - phase osmometry Two droplets on the thermistors One solution Another pure solvent Surrounding by so
Activities Just like real gases have fuga cities to describe deviations from perfect gas behav
7.6 The solvent activity Chemical potential of solvent (similar eqns set up for solute) Activity a A is a ki
7.6 The solvent activity All solvents obey Raoult’ s law, (p A / p A * = x A) as the concentration of the so
7.7 The solute activity The definition of activity coefficients and standard state for solutes is that they
(a) Ideal - dilute solutes A solute B (satisfying Henry’ s Law) has a pressure aspB = KBxB Where K Band p B *
(b) Real solutes Deviation from Henry’ s Law, use a B to place x B The standard state remains unchan
(c) Activities in terms of molalities We are free to choose a standard state. x B bB The standard state of μ ⊖ is when
(d) The biological standard state We can choose another standard state. pH = 7 is a standard state of H +, a H + 1
7.8 The activities of regular solutions γ A 1 asxB 0 and γ B 1 as x A 0 We have Δ mixG = nRT (xAlnxA + xBlnxB) For
(b) Excess function and regular Solutions For regular solution, the entropy of mixing has its ideal value. the nGE = HE Δ mix
7.8 The activities of regular solutions For a A = p A / p A * β = 0, ideal solution β > 0, endothermic mixing β < 0, exothe
Exercises (a) 7.11, 18,20, 22 Problems: 7.2, 12 Homework
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