CHAPTER 20.2 Electrochemistry

Review For the following reaction, determine which is being oxidized, which is being reduced, draw the voltaic cell, and label the anode, cathode, salt bridge, flow of electrons and voltmeter. **Write the standard cell notation for this reaction.

Half-Cells and Cell Potentials Batteries provide current to power lights and many kinds of electronic devices—such as the personal digital assistant shown here. You will learn how to calculate electrical potential.

Definitions The electrical potential of a cell results from a competition for electrons between two half-cells. The electrical potential of a voltaic cell is a measure of the cell’s ability to produce an electric current. The tendency of a given half-reaction to occur as a reduction is called the reduction potential.

Calculating the Cell Potential The difference between the reduction potentials of the two half-cells is called the cell potential.

Individual Half-Cell Potentials How are they measured? Using a standard hydrogen electrode with a potential of 0.000V. If we connect the standard hydrogen half-cell with all of the other half cells, we record that half-cells potential.

Example with Zinc What is Zinc’s half-cell potential?

Example with Zinc

Then we place all of the values in a table for you!! Table 21.2 Page 674 This will always be provided for you.

Calculating the cell Potential of a Redox Reaction If the calculated cell potential for a given redox reaction is positive, then the reaction is spontaneous as written. If the calculated cell potential is negative, then the reaction is nonspontaneous.

Calculating the Cell Potential of a Redox Reaction

You Try

Calculate Cell Potential

Determine the Cell Reaction But it looks like both are gaining electrons! How can we tell what is being reduced and oxidized? The half-cell with the more positive potential is where reduction is occurring. So we must flip the reaction being oxidized.

You try!

Practice Page 675 #10 Page 677 # 13 and 14 Page 676 # 11 Turn in to me when complete for your daily grade. We will have a quiz over today’s lesson next Thursday January 22. Unit 4 Part 2 Test will be Thursday January 29.