Electrochemistry involves chemical reactions in which electrons move from one element to another. The reactions that involve a transfer of electrons are called oxidation-reduction or redox reactions. Eight steps are required to balance redox equations: 1) dividing the reaction into half-reactions; 2) balancing elements other than oxygen and hydrogen; 3) balancing oxygen; 4) balancing hydrogen; 5) balancing the charges; 6) multiplying each half-reaction with coefficients to balance the number of electrons transferred; 7) adding the two half-equations; and 8) canceling common terms on both sides of the reaction. Redox reactions are important for galvanic cells, which are physical setups that separate the half-reactions of a redox reaction into two distinct areas connected by wire and a salt bridge. The standard reduction potential of each half-cell can be calculated so that the correct materials can be chosen for the galvanic cell. The Nernst equation can be used to find the cell potential, the electric potential of the entire cell, which can be used to determine the change in Gibbs free energy of the cell. Galvanic cells are commonly used in batteries and fuel cells. Corrosion is a natural process in which a redox reaction oxidizes a metal. Electrolysis is an industrial process in which electric current is used to split the components of an electrolyte into its constituent ions.
At A Glance
- During an oxidation-reduction reaction, electrons move from one element to another. The element that loses electrons is oxidized. The element that gains electrons is reduced.
Balancing oxidation-reduction reactions involves electron transfer and takes eight steps: dividing the reaction into half-reactions, balancing elements other than oxygen and hydrogen, balancing oxygen, balancing hydrogen, balancing the charges, multiplying each half-reaction with coefficients to balance the number of electrons transferred, adding the two half-equations, and canceling common terms on both sides of the reaction.
Galvanic cells, also called voltaic cells, are physical setups in which oxidation-reduction reactions can produce an electric current.
- The standard reduction potential, the tendency of the species to be reduced under standard conditions, can be measured in a galvanic cell.
The Nernst equation allows for the calculation of cell potential, which can be used to find the change in Gibbs free energy and determine whether a reaction is spontaneous.
- Galvanic cells are used as batteries and fuel cells to produce electrical power.
Corrosion is a natural oxidation-reduction reaction that occurs in metals. Atmospheric oxygen is the most common cathode in corrosion redox reactions.
Electrolysis is a process that uses electric current to do work on a chemical against its electric potential—in essence, the opposite of a galvanic cell.