Lecture 2511/2/05

Seminar today 5:30

TSB 006

Redox

Oxidation: Cu+ Cu+2 + e-

Reduction Fe3+ + e- Fe+2

Review: How to solve Redox

1) split into half cell reactions

2) Balance non-H, O atoms

3) Balance O with H2O

4) Balance H with H+

5) Balance charge with e-

6) Balance e’s and add equations

Practice: MnO4- + NO2

- Mn2+ + NO3-

Electrical charge (q)

q = moles x F

(coulombs) = moles x (coulombs/mole)

Faradays constant = 9.649 x 104 C/mol e’s

Electrical current (I)

Quantity of charge flowing per second through a circuit

Current = coulombs/sec= moles/sec x coulombs/mole= Ampere (A)

Electrical potential (E)

Measure of the work when an electrical charge moves from one point to another

Work = E x qJoules = volts x coulombs = J/coulombs x coulombs

Free Energy

G = - work = -E x q G = -nFE

Ohm’s Law

Current = Electrical potential /resistance I = E / R (amps) = Volts/Ohms (units) A = V / (units)

Power (P)

Work done per unit time J/s = Watts

P = work/s = E x q / s = E x I

Galvanic (voltaic) Cell

Uses a spontaneous chemical reaction to generate electricity

Need: Redox reaction Substance to be separated so e’s flow through

circuit

)s(Ag)aq(AgNO)aq()NO(Cd)s(Cd 323

One line = phase boundary

Two lines = salt bridge

Voltage Depends on

which elements and compounds are participating in the reaction

concentrations

CurrentDepends on size (# moles) of

elements/compounds

Standard potentials (E°)

All compounds are 1 bar or 1 M

Cell Potential

E°cell = E°cathode - E°anode

E°cell = E°red - E°ox

Standard Hydrogen Electrode (SHE)

Arbitrarily assigned E° = 0 V

Used to establish potential of other half-reactions

Pt(s),H2 (g, 1 atm)|H+ (aq, a=1)||

Standard Reduction Potential

1. Relative to SHE2. Reduction potential3. Reactants and products at standard state4. Independent of # of moles of reactants

and products shown in balanced half-reaction

1. Fe3+ + e- Fe2+ E° = +0.771 V2. 5Fe3+ + 5e- 5Fe2+ E° = +0.771 V

Nernst Equation

Way to express the driving force of a reaction Includes:

force at standard concentrations Modification term for reagent concentrations

Nernst Equation

Qlogn

V05916.0EE

Qlog303.2 Qln

C/mol96490F

K-mol V-Crmol) o J/(K3145.8R

QlnnF

RTEE

o

o

Nernst Equation

Fe3+ + e- Fe2+

]Fe[

]Fe[log

1

V05916.0771.0E

Qlogn

V05916.0EE

3

2

o