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Intro to Chemistry
Table of Contents
Unit 17 Overview: Electrochemistry
17.1 Review of Redox Chemistry
17.2 Galvanic Cells
17.3 Electrode and Cell Potentials
17.4 Potential, Free Energy, and Equilibrium
17.5 Batteries and Fuel Cells
17.6 Corrosion
17.7 Electrolysis

💏intro to chemistry review

17.3 Electrode and Cell Potentials

Citation:

Electrochemistry is all about the movement of electrons in chemical reactions. It's the science behind batteries, fuel cells, and even some industrial processes. Understanding how electrons flow between substances helps us harness electrical energy from chemical reactions.

Electrode potentials are key to predicting how chemicals will behave in these reactions. By comparing potentials, we can figure out which substances will give up electrons and which will grab them. This knowledge is crucial for designing better batteries and more efficient chemical processes.

Electrochemistry Fundamentals

Electrode and cell potentials

  • Electrode potential measures the tendency of a chemical species to gain electrons and be reduced
    • Determined relative to the standard hydrogen electrode (SHE) with a potential of 0 V
    • Reduction potentials are more positive and oxidation potentials are more negative
  • Cell potential ($E_{cell}$) represents the difference between the reduction potential of the cathode and the oxidation potential of the anode
    • Calculated using the equation: $E_{cell} = E_{cathode} - E_{anode}$
    • Positive $E_{cell}$ indicates a spontaneous redox reaction will occur
    • Cell potential is also referred to as voltage in electrochemical systems
  • Electrochemical cells consist of two half-cells, each containing an electrode and an electrolyte
    • Electrons flow from the anode (oxidation) to the cathode (reduction) through an external circuit
    • Salt bridge enables ion transfer to maintain charge balance between the half-cells
    • A galvanic cell (also known as a voltaic cell) is a type of electrochemical cell that produces electricity from spontaneous redox reactions

Oxidant vs reductant strengths

  • Standard reduction potentials measure the strength of an oxidizing agent
    • More positive reduction potentials signify stronger oxidizing agents (fluorine, chlorine)
  • Standard oxidation potentials measure the strength of a reducing agent
    • More negative oxidation potentials signify stronger reducing agents (alkali metals)
  • Comparing electrode potentials reveals that a species with a higher (more positive) reduction potential will oxidize a species with a lower (more negative) reduction potential
    • The species with the lower reduction potential acts as the reducing agent (anode)
  • The electrochemical series is a list of elements arranged according to their standard electrode potentials, helping predict the relative strengths of oxidizing and reducing agents

Calculating Cell Potentials and Predicting Spontaneity

Calculations with electrode potentials

  • Standard cell potential ($E^°_{cell}$) is calculated using standard reduction potentials ($E^°$) under standard conditions (25°C, 1 M concentrations, 1 atm pressure)
    • $E^°{cell} = E^°{cathode} - E^°_{anode}$
  • Spontaneity of redox reactions is determined by the sign of $E^°_{cell}$
    1. If $E^°_{cell} > 0$, the redox reaction is spontaneous under standard conditions
    2. If $E^°_{cell} < 0$, the redox reaction is non-spontaneous under standard conditions
    3. If $E^°_{cell} = 0$, the system is at equilibrium
  • Nernst equation relates cell potential to standard cell potential and concentrations of reactants and products
    • $E_{cell} = E^°_{cell} - \frac{RT}{nF} \ln Q$, where $Q$ is the reaction quotient, $R$ is the gas constant, $T$ is the temperature, $n$ is the number of electrons transferred, and $F$ is Faraday's constant
    • Allows for the calculation of cell potentials under non-standard conditions (varying concentrations, temperatures)

Electrochemistry Applications

  • Electrochemistry is the study of chemical processes that cause electrons to move, resulting in the interconversion between chemical and electrical energy
  • Applications include batteries, fuel cells, and electroplating processes
  • Understanding electrode and cell potentials is crucial for designing and optimizing electrochemical systems

Key Terms to Review (41)

Active electrodes: Active electrodes are the electrodes in an electrochemical cell where the redox reactions occur. They participate directly in the chemical reactions by either gaining or losing electrons.
Anode: The anode is the electrode where oxidation occurs in a galvanic cell. It is typically the negative terminal in such cells.
Cell potentials, Ecell: Cell potential, denoted as $E_{cell}$, is the measure of the electromotive force (emf) of an electrochemical cell. It represents the potential difference between the two electrodes.
Electrode potential (EX): Electrode potential is the voltage developed by an electrode in an electrochemical cell relative to a standard reference electrode. It indicates the tendency of a chemical species to gain or lose electrons.
Electrolytes: Electrolytes are substances that dissociate into ions when dissolved in water, allowing the solution to conduct electricity. Common examples include salts, acids, and bases.
Galvanic cells: Galvanic cells, also known as voltaic cells, are electrochemical cells that convert chemical energy into electrical energy through spontaneous redox reactions. They consist of two half-cells connected by a salt bridge and an external circuit.
Oxidizing agent (oxidant): An oxidizing agent, or oxidant, is a substance that gains electrons in a chemical reaction and, in the process, causes another substance to be oxidized. It is reduced while the other substance is oxidized.
Reducing agent (reductant): A reducing agent (reductant) is a substance that donates electrons to another substance in a chemical reaction, thereby reducing the oxidation state of the latter. It itself gets oxidized in the process.
Reaction quotient (Q): The reaction quotient, Q, is a measure of the relative amounts of products and reactants present in a reaction mixture at any given point in time. It is calculated using the same expression as the equilibrium constant but with current concentrations or partial pressures.
Standard hydrogen electrode (SHE): The standard hydrogen electrode (SHE) is a reference electrode with a defined potential of 0 volts under standard conditions. It consists of a platinum electrode in contact with 1 M H\textsuperscript{+} ions and hydrogen gas at 1 atm pressure.
Voltaic cells: Voltaic cells, also known as galvanic cells, are electrochemical cells that convert chemical energy into electrical energy through spontaneous redox reactions. They consist of two different metals connected by a salt bridge or porous membrane.
Standard electrode potential, E°X: The standard electrode potential, denoted as $E^\circ$, is the measure of the individual potential of a reversible electrode at standard state conditions, which are 1 M concentration for solutions, 1 atm pressure for gases, and pure solids or liquids. It is typically measured against the standard hydrogen electrode (SHE), which is assigned a potential of 0 volts.
Oxidation Potential: Oxidation potential, also known as redox potential, is a measure of the tendency of a chemical species to acquire electrons and undergo reduction. It is a fundamental concept in electrochemistry and is closely related to the reactivity and stability of chemical compounds.
Reaction Quotient: The reaction quotient, denoted as Q, is a measure of the relative concentrations of the products and reactants in a chemical reaction at any given time, regardless of whether the system has reached equilibrium or not. It is a useful tool for understanding the direction and extent of a reaction as it progresses towards equilibrium.
Standard Reduction Potential: The standard reduction potential, also known as the standard electrode potential, is a measure of the tendency of a chemical species to acquire electrons and be reduced. It is a fundamental concept in electrochemistry that helps determine the spontaneity and direction of redox reactions.
Oxidizing Agent: An oxidizing agent, also known as an oxidant, is a substance that has the ability to oxidize other substances by accepting electrons during a chemical reaction. Oxidizing agents are central to the understanding of redox chemistry and the functioning of electrochemical cells.
Reducing Agent: A reducing agent, also known as a reductant, is a substance that has the ability to reduce other substances by donating electrons in a chemical reaction. It is a key concept in the understanding of redox (reduction-oxidation) chemistry and the functioning of electrochemical cells.
Electrochemistry: Electrochemistry is the study of the relationship between electrical energy and chemical energy, and the interconversion between the two. It involves the study of chemical reactions that produce electricity and the use of electrical energy to drive chemical reactions.
Galvanic Cell: A galvanic cell, also known as a voltaic cell, is an electrochemical cell that generates an electric current through a spontaneous redox (reduction-oxidation) reaction. It is a device that converts the chemical energy of a spontaneous redox reaction into electrical energy.
Voltaic Cell: A voltaic cell, also known as a galvanic cell, is an electrochemical cell that generates an electric current from a spontaneous redox reaction. It consists of two different metallic electrodes immersed in an electrolyte solution, where one electrode undergoes oxidation (the anode) and the other undergoes reduction (the cathode), creating a potential difference that drives the flow of electrons and generates an electric current.
Electrode Potential: Electrode potential is the potential difference that arises between an electrode and the solution in which it is immersed. It is a measure of the tendency of an electrode to lose or gain electrons, and it is a crucial concept in electrochemistry and the understanding of electrochemical cells.
E_{cell}: E_{cell}, or the cell potential, is a measure of the driving force for a spontaneous electrochemical reaction to occur in a galvanic or voltaic cell. It represents the potential difference between the two electrodes in the cell and is a crucial parameter in understanding and predicting the behavior of electrochemical systems.
Half-cell: A half-cell is an electrochemical system that consists of a metal or ion in contact with a solution containing its own ions. It is one of the two essential components that make up an electrochemical cell, the other being the other half-cell. The potential difference between the two half-cells is what generates the cell potential, which is a crucial concept in understanding electrode and cell potentials.
Faraday's Constant: Faraday's constant is a fundamental physical constant that represents the amount of electric charge carried by one mole of electrons. It is a crucial parameter in electrochemical processes and is essential for understanding the relationship between electrical and chemical quantities.
Standard Hydrogen Electrode (SHE): The standard hydrogen electrode (SHE) is a reference electrode used to measure the reduction potential of other electrodes in electrochemical cells. It serves as the standard against which all other electrode potentials are measured and defined.
Voltage: Voltage, also known as electrical potential difference, is the driving force that pushes electric charge through a circuit. It is the measure of the potential energy difference between two points in an electrical system, and it is the key factor that determines the flow of electric current.
Reduction Potential: Reduction potential, also known as redox potential, is a measure of the tendency of a chemical species to acquire electrons and be reduced. It is a fundamental concept in electrochemistry and is used to predict the spontaneity and direction of redox reactions.
Redox Reaction: A redox (reduction-oxidation) reaction is a type of chemical reaction that involves the transfer of electrons between two or more reactants. In a redox reaction, one reactant is oxidized (loses electrons) while another is reduced (gains electrons), resulting in the conversion of chemical species and the release or absorption of energy.
E^°_{cell}: E^°_{cell}, also known as the standard cell potential or standard reduction potential, is a fundamental concept in electrochemistry that quantifies the ability of a redox reaction to produce an electric potential or voltage. It represents the potential difference between the standard reduction potentials of the cathode and anode half-reactions in an electrochemical cell under standard conditions.
E°: E° is the standard reduction potential, a measure of the tendency of a chemical species to acquire electrons and be reduced. It represents the potential difference between a half-reaction and the standard hydrogen electrode under standard conditions of temperature, pressure, and concentration.
Nernst Equation: The Nernst equation is a fundamental relationship in electrochemistry that describes the relationship between the reduction potential of an electrochemical half-reaction and the activities of the chemical species involved. It is a crucial tool for understanding and predicting the behavior of galvanic cells, electrode potentials, and the spontaneity of electrochemical processes.
Electrochemical Series: The electrochemical series, also known as the activity series or reactivity series, is a ranking of elements based on their tendency to lose or gain electrons during chemical reactions. This series is a fundamental concept in the understanding of galvanic cells and electrode potentials.
Anode: The anode is the electrode in an electrochemical cell where oxidation occurs, and electrons are released to flow through an external circuit. It is the negatively charged electrode that attracts positively charged ions and initiates the flow of electrons in a redox reaction.
Cell Potential: Cell potential, also known as electrochemical potential or redox potential, is a measure of the driving force or tendency for a chemical reaction to occur in an electrochemical cell. It represents the potential difference between the two electrodes in a galvanic cell, which determines the spontaneity and direction of the redox reaction.
E_{cathode}: E_{cathode} refers to the electrode potential of the cathode, which is the reduction half-reaction that occurs at the cathode in an electrochemical cell. The cathode is the electrode where reduction takes place, and its electrode potential is a measure of the tendency of the species at the cathode to be reduced.
E_{anode}: E_{anode} represents the anode potential, which is the potential difference between the anode of an electrochemical cell and a standard reference electrode, typically the standard hydrogen electrode (SHE). The anode potential is an important parameter in understanding and analyzing the behavior of electrochemical cells and their ability to generate or store electrical energy.
Standard Oxidation Potential: The standard oxidation potential, also known as the standard reduction potential, is a measure of the tendency of a chemical species to acquire electrons and be reduced. It is a fundamental concept in electrochemistry that quantifies the reducing or oxidizing strength of a given substance.
Electrolyte: An electrolyte is a substance that, when dissolved in a solvent such as water, dissociates into charged particles called ions. These ions are capable of conducting electricity and are essential for various chemical and physiological processes in the body and in electrochemical devices.
Electrochemical Cell: An electrochemical cell is a device that converts the free energy of a spontaneous redox reaction into electrical energy. It consists of two half-cells, each containing an electrode and an electrolyte solution, which are connected by an external circuit and an internal ionic conductor known as a salt bridge.
Electrode: An electrode is a conductor used to make contact with a nonmetallic part of an electrical circuit, such as an electrolyte solution or a semiconductor. It is a critical component in various electrochemical processes, including those involved in batteries, fuel cells, and the measurement of cell potentials.
Cathode: A cathode is an electrode where reduction occurs during an electrochemical reaction. It plays a crucial role in various processes such as galvanic cells, where it attracts cations from the electrolyte, facilitating the flow of electric current. Understanding the function of the cathode is essential for grasping concepts like electrode potentials and energy transformations in electrochemical cells.