electrochemistry n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Electrochemistry PowerPoint Presentation
Download Presentation
Electrochemistry

Loading in 2 Seconds...

play fullscreen
1 / 27

Electrochemistry - PowerPoint PPT Presentation


  • 62 Views
  • Uploaded on

Electrochemistry. Chapter 17. Electrochemistry. _____________________ – A process in which an element attains a more positive oxidation state Na(s)  Na + + e - ______________________ – A process in which an element attains a more negative oxidation state Cl 2 + 2e -  2Cl -.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Electrochemistry' - elin


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
electrochemistry1
Electrochemistry
  • _____________________– A process in which an element attains a more positive oxidation state

Na(s)  Na+ + e-

  • ______________________– A process in which an element attains a more negative oxidation state

Cl2 + 2e- 2Cl-

electrochemistry2
Electrochemistry

An old memory device for oxidation and reduction goes like this…

LEOsaysGER

LoseElectrons =____________

GainElectrons=____________

electrochemistry3
Electrochemistry
  • _______________________

The substance that is reduced is the oxidizing agent

  • _______________________

The substance that is oxidized is the reducing agent

electrochemistry4
Electrochemistry
  • _______________

The electrode where oxidation occurs

  • _______________

The electrode where reduction occurs

Memory device:

Reduction

at the

Cathode

galvanic cells1
Galvanic Cells
  • A device in which chemical energy is changed to ______________________ energy. (Opposite is called electrolysis)
  • The solutions must be connected so ions can flow to keep the net charge zero. A __________________________(a U-tube filled with an electrolyte) is used to connect the solutions.
  • ______________________ is used to measure the cell potential (Ecell)
table of reduction potentials
Table of Reduction Potentials

Measured against the StandardHydrogenElectrode

measuring standard electrode potential
Measuring Standard Electrode Potential

Potentials are measured against a hydrogen ion reduction reaction, which is arbitrarily assigned a potential of _______________________________.

standard reduction potentials
Standard Reduction Potentials

2H+(aq) + Zn(s)  Zn2+(aq) + H2(g)

The voltage measured for this cell is 0.76V. It is impossible to measure each separate half-reaction but if the standard hydrogen reduction (1 M H+ and 1 atm) is assigned a zero voltage then the standard zinc reaction occurring at the anode has a voltage of 0.76V.

galvanic electrochemical cells
Galvanic (Electrochemical) Cells

Spontaneous redox processes have:

A ________________

cell potential, E0

A _________________ free energy change, (-G)

zn cu galvanic cell
Zn - Cu Galvanic Cell

Zn2+ + 2e- Zn E =

Cu2+ + 2e-  Cu E =

From a table of reduction potentials:

zn cu galvanic cell1
Zn - Cu Galvanic Cell

The less positive, or more negative reduction potential becomes the oxidation…

example problem
Example Problem

Al3+ (aq) + Mg(s)  Al(s) + Mg2+ (aq)

Give the balanced chemical equation and Eo for the cell.

line notation
Line Notation

An abbreviated representation of an electrochemical cell

Anode

material

Cathode

material

Anode

solution

Cathode

solution

|

||

|

calculating g 0 for a cell
Calculating G0 for a Cell

n= moles of electrons in balanced redox equation

F=Faraday constant = ______________ coulombs/mol e-

Zn + Cu2+  Zn2+ + Cu E0= + 1.10 V

the nernst equation
The Nernst Equation

Standard potentials assume a concentration of 1 M. The Nernst equation allows us to calculate potential when the two cells are not 1.0 M.

R= 8.31 J/(molK)

T = Temperature in K

n = moles of electrons in balanced redox equation

F = Faraday constant = 96,485 coulombs/mol e-

nernst equation simplified
Nernst Equation Simplified

At 25 C (298 K) the Nernst Equation is simplified this way:

equilibrium constants and cell potential
Equilibrium Constants and Cell Potential

At equilibrium, forward and reverse reactions occur at equal rates, therefore:

  • The battery is __________________
  • The ____________________, E, is zero volts

Modifying the Nernst Equation (at 25 C):

concentration cell
Concentration Cell

???

Both sides have the same components but at different concentrations.

Step 1: Determine which side undergoes oxidation, and which side undergoes reduction.

concentration cell1
Concentration Cell

???

Both sides have the same components but at different concentrations.

Anode

Cathode

The 1.0 M Zn2+ must decrease in concentration, and the 0.10 M Zn2+ must increase in concentration

concentration cell2
Concentration Cell

Concentration Cell

???

Both sides have the same components but at different concentrations.

Anode

Cathode

Step 2: Calculate cell potential using the Nernst

Equation (assuming 25 C).

nernst calculations
Nernst Calculations

Zn2+ (1.0M)  Zn2+ (0.10M)

electrolytic processes
Electrolytic Processes

Electrolytic processes are NOT spontaneous. They have:

electrolysis of water
Electrolysis of Water

In acidic solution

Anode rxn:

-1.23 V

Cathode rxn:

-0.83 V

electroplating of silver
Electroplating of Silver

Anode reaction:

Cathode reaction:

Electroplating requirements:

1. Solution of the plating metal

2. Anode made of the plating metal

3. Cathode with the object to be plated

4. Source of current

solving an electroplating problem
Solving an Electroplating Problem

How many seconds will it take to plate out 5.0 grams of silver from a solution of AgNO3 using a 20.0 Ampere current?

Ag+ + e-  Ag