页数：44页文件大小：2.12 MB来源： Atkins’PhysChem物理化学ppt课件
本课件深入平衡电化学：先用德拜-休克尔极限公式处理离子活度与离子强度，再介绍各类电池与电动势测定方法，给出标准电极电势、参比电极与电化学序列，并用能斯特方程计算电池电动势。
Thermodynamic functions of ions in solution Electrochemical cell Half - reactions and electrodes Thermodynamic functions of formation I on activities Varieties of cell Standard potentials Applications of standard potential The electrochemical series The meas
The activity relates to the molalitybvia 10.2 I on activities a = γ b / b where γ is the activity coefficient
平衡电化学
Since there is no experimental way to separate the product (γ + γ -) into contributions from the cations and anions, γ ± is introduced here to assign equal responsibility for non - ideality to both kind of ions. (b) mean activity coefficients γ ± = (γ + γ -) ½ Consider an electrica
The chemical potential for individual ionsM + and X - then becomes: (b) mean activity coefficients For a general compound of the following
平衡电化学
The long range and strength of the Coulombic interaction between ions means that it is likely to be the primarily responsible for the departures from ideality in ionic solutions and to dominate all the other contributions to non - ideality.
This is the basis of the Debye - H ü ckel theory of ionic solutions. (c) The Debye - H ü ckel law Ionic atmosphere 6
Debye - H ü ckel limiting law is employed to calculate the mean activity coefficient: (c) The Debye - H ü ckel law Where A = 0.509 for aqueous solution at 2
Solutions contain more than one types of electrolytes (c) The Debye - H ü ckel law The ionic strength of the solution equals
. 050 mol kg - 1 K 3 [Fe (C N) 6] (a q), 0.040 mol kg - 1 NaCl (a q), and 0.03 mol kg - 1 Ce (SO 4) 2 (a q) (c) The Debye - H ü ckel law I (NaCl) = ½ {12 0.04 + (- 1) 2 0.04}
Calculating the mean activity coefficient (c) The Debye - H ü ckel law Solution: In order to calculate the mean
Calculating the mean activity coefficient (c) The Debye - H ü ckel law 2.0 m mol kg - 1 C a (NO 3) 2 at 25 o C.
(d) Experimental test of The Debye - H ü ckel law 14
活度系数 例题
Example: The mean activity coefficient in a 0.100 mol kg - 1 MnCl 2 (a q) solution is 0.47 at 25 o C. What is the percentage error in the value predicted by the Debye - H ü ckel limiting law? (e) Accuracy of the Debye - H ü ckel limiting law I (MnCl 2) = ½ ((2)
When the ionic strength of the solution is too high for the limiting law to be valid, the activity coefficient maybe estimated from The extended Debye - H ü ckel law: (f) Extended Debye - H ü ckel limiting law B is an adjustable empirica
Calculating parameter B (f) Extended Debye - H ü ckel limiting law Example: The mean activity
Electrochemical cell Electrochemical cells Two electrodes or metallic conductors Ionic cond
Two types of electrochemical cells: 10.3 Half - reactions and electrodes 1. Galvanic cell: is an electroch
Other important concepts include: 10.3 Half - reactions and electrodes Oxidation: the removal of electro
Two type of electrodes: 10.3 Half - reactions and electrodes Anode: the electrode at which oxi
Varieties of electrodes: 10.3 Half - reactions and electrodes Half - reaction Redox couple desi
Both redox and non - redox reactions can be expressed as the difference of two reduction half reactions: 10.3 Half - reactions and electrode sSn 2 + + 2 Fe 3 + S n 4 + + Fe
(b) Reactions at electrodes 10.3 Half - reactions and electrodes Red 1 → O x 1 + ν e - at anode Ox
10.3 Half - reactions and electrodes 28
The simplest type of cell has a single electrolyte (left). In some cases it is necessary to immerse the electrodes in different electrolytes, as in “ Daniell cell ” (right). 10.4 Varieties of cells 29
电池的类型
In an electrolyte concentration cell (电解质浓差电池), the electrode compartments are identical except for the concentrations of the electrolytes. In an electrode concentration cell (电极浓差电池) the electrodes themselves have different concentrations, either because they are gas electrodes operating at different pressures or because they are amalgams (汞齐) with different concentrations.
10.4 Varieties of cells 30
(a) Liquid junction potential: 10.4 Varieties of cells Due to the difference in the concentns of elec
Electrochemical cells If two compartment, they may be joined by a salt
(b) Notation 10.4 Varieties of cells The right - hand side electrochemical cell is
In the above cell, we can trace the movement of charge (b) Notation
For the right Fig., the “ cell diagram ”: (b) Notation An electrolyte concentration cellPt (s) | H 2 (g) | HCl (
(c) The cell reaction Right: C u 2 + (a q) + 2 e - → C u (s) Pt (s) |
(d) The cell potential Electromotive force, (emf): E Maximum electrica
(e) The Relationship between E and ∆ r G ∆ r G = - ν F E Relationship
(e) The Relationship between E and ∆ r G 39
(f) The Nernst equation Relationship between ∆ r G and the composition
(f) The Nernst equation The variation ofemf with the value of the reac
(g) Electrolyte Concentration Cells M | M + (a q, L) | | M + (a q, R)
(h) Cells at equilibrium Under equilibrium condition: Q = K, and E = 0
Exercises Exercises (a) 10.7, 10, 12, 15, 16 Discussion: problem 10.24
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