Applications of Voltaic Cells

Size: px

Start display at page:

Download "Applications of Voltaic Cells"

Susanna Burke
5 years ago
Views:

Dry Cells Since voltaic cells are not portable, dry cells were developed.

1 Applications of Voltaic Cells Lesson 4 chapter 13 Objective You will be able to explain how the development of the voltaic cell had affected society. Dry Cells Since voltaic cells are not portable, dry cells were developed. These cells have an electrolyte that is thickened into a paste, but can still allow electrons to move. Dry cells are batteries

2 example Cathode Reaction MnO 2(s) + H 2 O (l) + 2 e - Mn 2 O 3(s) + 2 OH - (aq) Anode Reaction Zn (s) Zn e - Button Battery

3 Features of a Dry Cell Dry cells stop producing electrical energy when the reactants are used up A battery is a set of voltaic cells connected in series Example: a 9 volt battery is really six 1.5 volt dry cells connected in series (In a series connection, the negative electrode of one cell is connected to the positive electrode of another cell) A primary cell is one that cannot be recharged. A secondary cell can be recharged Electrical energy is used to reverse the reaction in the cell and replenish the reactants We will focus on primary cells.

Lead acid car battery: secondary cell Cathode is lead (IV) oxide Reaction: Anode is lead Reaction: Cathode When your is lead car (IV) is running, oxide an electric current, produced by the

4 Lead acid car battery: secondary cell Cathode is lead (IV) oxide Reaction: Anode is lead Reaction: Cathode When your is lead car (IV) is running, oxide an electric current, produced by the alternator, reverses the cathode Reaction? and anode reactions. Anode is lead This replenishes the reactants so the battery does not go dead Reaction? When your car is running, an electric current, produced by the alternator, reverses the cathode and anode reactions. This replenishes the reactants so the battery does not go dead

Fuel Cells A battery that can be refueled They are designed so the reactants flow into the cell, and the products flow out Fuel cells are more efficient than combustion engines or generators and do

5 Fuel Cells A battery that can be refueled They are designed so the reactants flow into the cell, and the products flow out Fuel cells are more efficient than combustion engines or generators and do not produce greenhouse gases or other polluting gases Cathode: O 2(g) + 4 H e - 2 H 2 O Anode: H 2(g) 2 H e - Net Reaction 2 H 2(g) + O 2(g) 2 H 2 O (l) What is the cell potential for the hydrogen fuel cell?

6 The fuel cell provides a highly efficient conversion of the chemical energy in hydrogen, natural gas, or hydrocarbons into electrical energy, and because of their high energy density (energy per unit weight of the power source), fuel cells are superior to batteries in portable equipment. Corrosion Corrosion is a spontaneous redox reaction of a metal with substances in the environment Metals can be oxidized by the oxygen in our atmosphere Rust is produced when iron is oxidized to form Fe 2 O 3 x H 2 O The surface of a piece of iron acts like a voltaic cell

Anode Iron Cathode Inert material (usually impurity in the iron) Cathode: O 2 + 2 H 2 O + 4 e - 4 OH - Anode: Fe Fe 2+ + 2 e - Net: 2 Fe + O 2 + 2 H 2 O 2 Fe(OH) 2(s) The Fe(OH) 2(s) further reacts

7 Anode Iron Cathode Inert material (usually impurity in the iron) Cathode: O H 2 O + 4 e - 4 OH - Anode: Fe Fe e - Net: 2 Fe + O H 2 O 2 Fe(OH) 2(s) The Fe(OH) 2(s) further reacts to form Fe O x H O Prevention Paint or enamel coatings prevent air and water from reaching the metal. Galvanizing Covering iron with zinc Zinc is more reactive than iron (SRA) so it will be oxidized instead of iron, making a coating that protects the iron. Cathodic Protection Attaching a more reactive metal to an iron object (Al, Mg, Zn) The more reactive metal is oxidized instead of the iron (sometimes called a sacrificial anode) Must be periodically replaced as they are used up

An advantage of sacrificial anode systems is the flexibility in application. Anodes can be installed in a variety of applications and configurations.

8 An advantage of sacrificial anode systems is the flexibility in application. Anodes can be installed in a variety of applications and configurations. No outside power is required for cathodic protection to be effective. Another advantage is the minimal maintenance required for these systems to function. Assignment Read text p Do review questions #1-5,8,13,14.

Lecture Presentation. Chapter 20. Electrochemistry. James F. Kirby Quinnipiac University Hamden, CT Pearson Education, Inc.

Lecture Presentation. Chapter 20. Electrochemistry. James F. Kirby Quinnipiac University Hamden, CT Pearson Education, Inc. Lecture Presentation Chapter 20 James F. Kirby Quinnipiac University Hamden, CT is the study of the relationships between electricity and chemical reactions. It includes the study of both spontaneous and