Chapter 20

Review section 4.4 of the textbook, especially the Oxidation numbers rules on page 137.

Chemistry is an experimental science where measurements are made. The theories and equations we see in the text are backed up by experimental results. The following example in the video below helped shape Electrochemistry.

20.1 Electrochemistry Observations

Electrochemistry is the study of chemical and electrical energy. The two processes we will discuss are the generation of an electrical current from a chemical (redox) reaction (this is a spontaneous process) and the use of an electric current to produce a chemical change (a nonspontaneous process).

20.1 Electrochemistry

Now that we have observed various electrochemical processes, we need a convention to describe each voltaic cell.

20.3 Silver-Copper Voltaic Cell Part 1

20.3 Silver-Copper Voltaic Cell Part 2

20.3 Silver-Iron Voltaic Cell

When you describe voltaic cells, be sure to keep a few things in mind:
*When a half reaction is reversed, the sign of the standard cell potential is reversed.
*The standard cell potential is an intensive property.
*To run spontaneously, the standard cell potential must be positive.
*A chemically inert conductor is required if none of the substances participating in the half reaction is a conducting solid.

20.3 Voltaic Cells

Now that we have investigated Voltaic Cells, we need at come up with a convention to balance the reactions occurring in these cells.

20.2 Balancing Redox Reactions

Work can be done when electrons are transferred through a wire. The amount of work depends on the potential difference between the anode and cathode, and we can determine the relationship between the Cell Potential and the Gibbs Free Energy.

20.5 Ecell and Delta G (part 1)

20.5 Ecell and Delta G (part 2)

All the calculations to this point have been calculated under standard conditions. When the concentrations of the solutions in the anode and cathode compartment are changed, the cell potential will change. This relationship, referred to as the Nerst equation, will allow us to calculate the cell potential under non-standard conditions.

20.6 Cell Potential and Concentration

20.6 Application of Nerst Equation

In a Galvanic/Voltaic Cell, a spontaneous redox reaction produces a current (electricity). In an electrolytic cell, electrical energy is needed to produce a chemical change. During electrolysis, the electrical energy forces a non-spontaneous reaction to occur.

20.9 Electrolysis

In an electrolytic process, we can use the stoichiometric relationships of an electrolytic process to calculate various electrolytic properties. In the first example shown below, we will calculate the mass of solid copper that is plated when a current of 10 amps is passed for 30 minutes through a Cu2+(aq) solution.

20.9 Stoich of Electrolytic Processes

The next example shows how long a current of 5 amps must be applied to a solution of Ag+ to produce 10.5 grams of Ag(s).

20.9 Electrolysis Example

Producing H2(g) has gained widespread attention from its potential application as a source of alternate energy. The following example shows why the electrolysis of water is not an effective way to produce hydrogen gas and shows how much hydrogen gas is liberated during the passage of 2 amps for 30 minutes.

20.9 Electrolysis of H2O

We can also calculate the concentration of a particular ion remaining in a solution after a current has been passed through its solution. In this case, the [Cu2+] remaining in 335 mL of solution that was originally 0.215 M copper(II) sulfate after the passage of 2.17 amps for 235 seconds, can be calculated.

20.9 Calculating Concentration in Electrolysis

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