Textbook Notes (368,317)
Canada (161,798)
Chemistry (261)
CHEM 1A03 (89)
Chapter 20

Lecture and Textbook Collaborated Notes - Chapter 20 - CHEM 1A03
Premium

5 Pages
72 Views
Unlock Document

Department
Chemistry
Course
CHEM 1A03
Professor
Aadil Merali Juma
Semester
Fall

Description
Chem 1A03 Chapter 20: Electrochemistry 20.1 Electrode Potentials and Their Measurement Redox Reactions: Examples a) Spontaneous: Cu + 2 Ag+ Cu + 2 Ag b) Non-spontaneous: Cu + Zn  no reaction + Electrochemical Cells: Cu/Ag  An electrode immersed in a solution containing the same metal, M , is called a half cell  Two connected half cells  The 2 half reactions are separated, yet connected electrically (salt bridge, external wire) o Charge is carried by ions, so a wire cannot be used o Anions (NO 3 migrate from the salt bridge into the copper half cell to neutralize the excess positive charge from the Cu ions + o Cations (K ) migrate from the salt bridge into the silver half cell to neutralize the excess negative charge from the NO 3ons  Solid metals = electrodes (anode, cathode), M -  Movement of e from anode to cathode generates violated  Movement of cations and anions through salt bridge maintains electro neutrality in solution n+ -  Oxidation (anode) – surface of electrode erodes as M are produced; n e then travels to cathode o M  M + n e - 2+ - o Cu(s)Cu ( aq) 2 e  Reduction (cathode) – cathode gains mass as M ions gain n e and form M(s) o M + n e  M + - o 2 Ag (aq) 2e  2 Ag (s)  Remember – “an ox and a red cat” anode ox, reduce cathode; or vowels OA, consonants CR + 2+  Overall Cell Reaction: Cu(s)2 Ag (aq) Cu ( aq)+ 2 Ag (s)  Galvanic (voltaic) cell – results from spontaneous chemical reactions  Electrolytic cell – uses electricity to accomplish non-spontaneous chemical change  Cell voltage, or potential difference between two half cells o Measured in volts (V), the energy per unit charge  Potential difference of one volt signifies an energy of one joule for every coulomb of charge passing through an electric circuit; 1 V = 1 J/C o Driving force for electrons – the greater the voltage, the greater the dirving force o Also called electromotive force (emf) or cell potential – represented by the symbol Ecell Cell Diagrams – shows the components of an electrochemical cell in a symbolic way  Symbolic notation of cell:  Sometimes an electrode is inert (does not chemically participate, but is needed for electron transfer to occur Chem 1A03 20.2 Standard Electrode Potentials Standard Electrode Potentials  Absolute half-cell potentials cannot be measured  All potentials are measured relative to the standard hydrogen electrode (SHE); assigned a potential of 0V o Involves equilibrium established on the surface of an inert metal between H O io3s from a solution in which they are at unit activity (that is, a = 1) and H molecules from the gaseous state at a pressure H3O+ 2 of 1 bar o 2 H (a=1) + 2 e  H (2, 1 bar) E° = exactly 0 V (volt) Simplify: a = 1 becomes [H+] = 1M; 1 bar = 1 atm o Half-cell diagram: Pt(s) | H2(g, 1 atm) | H (aq, 1M)  3 phases are present – solid platinum, gaseous hydrogen and aqueous hydrogen ion  Standard electrode potentials (E°) measures the tendency for reduction to occur (E° ) atred electrode  Standard conditions: Conc. = 1M, pressures = 1 atm Standard Cell Potentials (E° cell  E°cell voltage of a cell formed from 2 standard electrodes  Can be expressed as E°(cathode right= - E°(anode left ALTERNATIVELY  For a given half-cell we can say E°ox -E° red (reverse the sign on the potential for the oxidation half cell) 2+  Eg/ Zn /Zn E° red - 0.763, therefore E° ox+ 0.763  E° cell E°red+ E°ox  Note: A standard potential is an intensive property – it does not depend on the amount of substance reacting  We do not multiply E° redor E°oxy a factor even if we multiply a half-reaction by a factor when balancing  E°cell 0 = spontaneous  Magnitude of cell potential indicated driving force for cell o Eg/under standard conditions Oxidation of metallic Zn by Cu (E° cell 1.100V) has a greater tendency to go to completion than does + oxidation of metallic Cu by Ag ions (E° cell 0.4600V) Standard Reduction Potentials (E° ) red  Table 20.1: Selected Standard Electrode (Reduction) Potentials at 25°, page 872  Species most easily reduced on left side, at most positive potential  Species most easily oxidized on right side, at least positive potential Chem 1A03 20.3 E cellΔG and K Spontaneity: E°cell and ΔG°  Electrical work is done when a reaction occurs in a voltaic cell; product of three terms o Ecell;ectromotive force or cell potential o z; the number of electrons transferred between the electrodes  electron number (charge number) of an electrochemical reaction, no units o F; Faradays constant, the electric charge per mole of electrons; 96,485 coulombs/mol of electrons (C/mol)  joule = volt x coulomb (or volt = energy/unit charge)  w elec zFEcell o Only applies if the cell operates reversibly (requires
More Less

Related notes for CHEM 1A03

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit