山东大学：《物理化学》课程教学资源（讲义资料）7.7 Electromotive force-for students

87.7 Thermodynamics of reversible cell Out-class extensive reading Ira N. Levine, pp. 294-310 Section 10.10 standard-state thermodynamic properties of solution components pp.426 Section 14.6 thermodynamics of galvanic cells

§7.7 Thermodynamics of reversible cell Out-class extensive reading: Ira N. Levine, pp. 294-310 Section 10.10 standard-state thermodynamic properties of solution components pp. 426 Section 14.6 thermodynamics of galvanic cells

87. 7 Thermodynamics of reversible cell Goals of this class (1)Understand the principle for determining EMF: high input voltmeter and compensation 2)Demonstrate the component of Weston standard cell (3 )Nernst equation: theoretical deduction and application (4) Apply the principle for determining thermodynamic quantities from electrochemical measurements (5)Explain the principles of relative standard

Goals of this class: (1) Understand the principle for determining EMF: high input voltmeter and compensation. (2) Demonstrate the component of Weston standard cell; (3) Nernst equation: theoretical deduction and application; (4) Apply the principle for determining thermodynamic quantities from electrochemical measurements; (5) Explain the principles of relative standard; §7.7 Thermodynamics of reversible cell

7.7 Thermodynamics of reversible cell 7.7.1 Measurement of Electromotive forces(emfs) What is electromotive forces? Can voltameter be used to measure electromotive force? U E=(R+R)= R r+ E R 1+ Discussion E R R High-impedance input voltameter

7.7.1 Measurement of Electromotive forces (emf's) Can voltameter be used to measure electromotive force? E R R I o i = ( + ) Ro U I = U R R R E o o + i = o i R R U E = 1+ V E Ri Ro U Discussion What is electromotive forces? High-impedance input voltameter §7.7 Thermodynamics of reversible cell

7.7 Thermodynamics of reversible cell 7.7.1. Measurement of Electromotive forces(emfs) (1)Poggendorff's compensation method i=0, thermodynamic reversibility. E E --------A 一==== B A 1111 E E E w: working ce E E、: test cell Principle of potentiometer E: standard celll

(1) Poggendorff’s compensation method i = 0, thermodynamic reversibility. EW: working cell Ex : test cell Es : standard cell A Es Ex Principle of potentiometer G Ew Ex Es K A B C1 C2 7.7.1. Measurement of Electromotive forces (emf's) §7.7 Thermodynamics of reversible cell

87. 7 Thermodynamics of reversible cell 7.7.1. Measurement of Electromotive forces(emfs) (2) Weston standard cell The Weston cell, is a wet-chemical cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters. Invented by Edward Weston in 1893,it was adopted as the international Standard for emf between 1911 and 1990

(2) Weston standard cell The Weston cell, is a wet-chemical cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters. Invented by Edward Weston in 1893, it was adopted as the International Standard for EMF between 1911 and 1990. 7.7.1. Measurement of Electromotive forces (emf's) §7.7 Thermodynamics of reversible cell