Redox Reactions and Chemical Cells

Study Notes

Redox Reactions

Redox reactions involve the transfer of electrons between species.
Oxidation is the loss of electrons, and reduction is the gain of electrons.
Oxidizing agents are substances that cause oxidation (they are reduced).
Reducing agents are substances that cause reduction (they are oxidized).
Oxidizing and reducing agents are key components of redox reactions.
Half-reactions are used to illustrate redox reactions, and balance electron transfer.
In many redox reactions, species change oxidation states.
Oxidation state is a hypothetical charge that an atom would have if all bonds were ionic.
Rules for assigning oxidation states are helpful in identifying the species undergoing oxidation or reduction.
These rules are essential for balancing redox equations.

Chemical Cells

A galvanic (voltaic) cell uses a spontaneous redox reaction to generate electrical energy.
An electrolytic cell uses electrical energy to drive a non-spontaneous redox reaction.
Electrodes are the sites of electron transfer.
The anode is where oxidation occurs.
The cathode is where reduction occurs.

Components of a Galvanic Cell

Anode: The electrode where oxidation occurs, and electrons leave the cell.
Cathode: The electrode where reduction occurs, and electrons enter the cell.
Salt Bridge: A component in the galvanic cell. Permits ion flow between half-cells maintaining electrical neutrality.
Electrolyte: A solution that conducts ions.
External Circuit: The pathway for electrons to flow from the anode to the cathode.

Cell Potential

Cell potential (E°cell): A measure of the driving force for the reaction.
Cell potential is measured in volts.
Standard cell potential (E°cell) can predict if a redox reaction will be spontaneous.
The potential difference between the anode and cathode directly relates to the cell voltage.
Cell potentials are the difference in the standard reduction potentials for half-reactions.

Calculating Cell Potential

The standard cell potential is calculated by subtracting the standard reduction potential of the anode from the standard reduction potential of the cathode.
Standard reduction potentials are tabulated values.
The more positive half-reaction potential, the stronger the oxidizing agent.
The more negative half-reaction potential, the stronger the reducing agent.

Factors Affecting Cell Potential

Concentration of reactants and products affect cell potential: Changes in concentration affect the equilibrium of the redox reaction.
Temperature: Affects the kinetic rate of the reaction; higher temperature often increases reaction rate.
Pressure: While less significant in many electrochemical situations, pressure can be necessary for gas-phase reactants.

Applications of Electrochemical Cells

Batteries: Transform chemical energy into electrical energy.
Corrosion: An electrochemical process that deteriorates metals through oxidation-reduction reactions.
Electroplating: Using electricity to coat a metal with another metal.
Electrolysis: Non-spontaneous reactions driven by electricity.
Sensors: Monitoring or measuring concentration or presence of substances by electrochemical means; important in industrial and environmental science.

Description

Explore the fundamental concepts of redox reactions and chemical cells in this quiz. Understand the roles of oxidation and reduction, the significance of oxidizing and reducing agents, and how half-reactions illustrate electron transfer. Test your knowledge on galvanic and electrolytic cells.