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Electrochemistry - Voltaic Cells

Date Lecture/Activities Pg#

93. 05/19/15 Electrochemistry 154

Objective:

I will record lecture notes to identify how redox reaction are used to generate energy in voltaic and electrolytic cells.

Chemcatalyst:

1.Given reaction rate data for: F2(g) + 2ClO2(g) --> 2FClO2(g)

Experiment [F2](M) [ClO2](M) Initial Rate (M/s)

1 0.10 0.010 1.2 x 10-3

2 0.10 0.040 4.8 x 10-3

3 0.20 0.010 2.4 x 10-3

A. Determine the order of each reactant and the overall reaction order.

(Hint: [ ] = k x=order)

x

Voltaic Cells and Energy

Indicates the magnitude of the electromotive force, E° expressed in volts

Electrical Potential Energy

A measure of the amount of current that can be generated from a voltaic cell to do work

* Electric charge can flow between two points only when a difference in electric potential energy exists between two points.

*Electromotive forces push the electrons generated at the anode to the cathode

*Cell Potential: force produced by the difference in potential energy between the two electrodes (measured in volts)

*Voltage: determined by comparing the difference in the tendency of the two electrode materials to accept electrons

-the greater the difference, the greater the PE difference

between the two electrodes & the larger the voltage

complete the pathway between the beakers to allow electrical charge to flow

A pathway that maintains neutrality of the solution by allowing ions to pass back and forth

Calculating Electrochemical Cell Potentials

Reduction Potential

  • tendency of a substance to gain electrons
  • When two half-reactions are coupled, the voltage generated corresponds to the difference in potential between the half reactions. (determined experimentally)

Standard Hydrogen electrode

consist of a small sheet of platinum immersed in a hydrochloric acid solution that has a hydrogen-ion concentration of 1M. Hydrogen gas at a pressure of 1 atm is bubbled in and the temperature is maintained at 25 degrees celsius

Oxidation

Reduction

Redox in Electrochemistry

Electrochemistry

The study of the redox processes by which chemical energy is converted to electrical energy and vice versa

Redox Reactions

Involve the transfer of electrons from the oxidized species to the reduced species.

Oxidation - losing electrons (anode)

Reduction - gaining electrons (cathode)

2+

Zn (s) + Cu (aq) Zn (aq) + Cu (s)

Determining electrochemical cell potentials

Half Cells: parts of electrochemical cell that separate the oxidation and reduction reactions

Formula for Cell Potential

Use the values of the known Standard Reduction Potentials to calculate the overall Cell Potential

oxidation

reduction

Example Problem

Voltaic Cell : type of electrochemical cell that converts chemical energy to electrical energy by a spontaneous redox reaction

- -

2

-

2+

The following reduction half-reaction s represent the half-cells of a voltaic cell.

I (s) + 2e 2I (aq)

Fe (aq) + 2e Fe (s)

Determine the overall cell reaction and the standard cell potential. Describe the cell using cell notation.

* The half reaction with the lowest reduction potential will be the oxidation

* (+) values of cell potential: spontaneous

* (-) values of cell potential: not spontaneous

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