2.1 Electrochemistry basics and redox reactions

Electrochemistry basics and redox reactions are key to understanding how batteries work. These processes involve the transfer of electrons between species, creating electrical energy. Oxidation and reduction reactions form the foundation of electrochemical cells.

Electrochemical cells consist of electrodes, electrolytes, and the flow of electrons. Understanding the roles of anodes, cathodes, and electrolytes helps explain how batteries generate and store energy. This knowledge is crucial for developing better energy storage technologies.

Redox Reactions

Oxidation and Reduction Processes

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• Oxidation involves the loss of electrons from a species, resulting in an increase in its oxidation state
• Reduction involves the gain of electrons by a species, resulting in a decrease in its oxidation state
• Oxidizing agents are species that accept electrons and become reduced in the process (oxygen, halogens)
• Reducing agents are species that donate electrons and become oxidized in the process (metals, hydrogen)

Redox Reactions and Half-Cell Reactions

• Redox reactions involve the transfer of electrons between species, with one species being oxidized and the other reduced
• Redox reactions can be split into two half-reactions: the oxidation half-reaction and the reduction half-reaction
• In a redox reaction, the number of electrons lost by the species being oxidized must equal the number of electrons gained by the species being reduced
• Half-cell reactions are used to represent the individual oxidation and reduction processes occurring in a redox reaction (zinc oxidation, copper reduction)

Electrochemical Cell Components

Electrodes and Electrolyte

• Electrodes are conductive materials that allow the transfer of electrons to or from a species in an electrochemical cell (graphite, platinum)
• The electrolyte is a solution that contains ions and allows for the flow of electric current through the cell (aqueous solutions of salts, acids, or bases)
• The electrolyte facilitates the movement of ions between the electrodes to maintain charge balance
• The concentration and composition of the electrolyte can affect the performance and efficiency of the electrochemical cell

Anode and Cathode

• The anode is the electrode where oxidation occurs, and electrons are released into the external circuit
• The cathode is the electrode where reduction occurs, and electrons are consumed from the external circuit
• In a galvanic cell, the anode is the negative electrode, and the cathode is the positive electrode
• In an electrolytic cell, the anode is the positive electrode, and the cathode is the negative electrode

Electrochemical Thermodynamics

Standard Electrode Potential

• The standard electrode potential $(E^0)$ is a measure of the tendency of a species to be reduced under standard conditions (1 M concentration, 1 atm pressure, 25°C)
• Standard electrode potentials are determined relative to the standard hydrogen electrode (SHE), which has an assigned potential of 0 V
• Species with more positive standard electrode potentials have a greater tendency to be reduced, while those with more negative potentials have a greater tendency to be oxidized
• Standard electrode potentials can be used to predict the spontaneity and direction of redox reactions (copper and zinc half-cells)

Nernst Equation

• The Nernst equation relates the electrode potential to the concentrations of the species involved in the redox reaction and the standard electrode potential
• The Nernst equation is given by: $E = E^0 - \frac{RT}{nF} \ln Q$, where $E$ is the electrode potential, $E^0$ is the standard electrode potential, $R$ is the gas constant, $T$ is the temperature, $n$ is the number of electrons transferred, $F$ is Faraday's constant, and $Q$ is the reaction quotient
• The Nernst equation allows for the calculation of the electrode potential under non-standard conditions
• The Nernst equation can be used to determine the equilibrium constant and the direction of a redox reaction (concentration cell)