| Term | Definition |
|---|---|
| cell potential | The electrical potential difference between the anode and cathode of an electrochemical cell, which drives the spontaneous redox reaction. |
| concentration cell | An electrochemical cell in which the two half-cells contain the same chemical species but at different concentrations. |
| equilibrium | The state in which the forward and reverse reaction rates are equal, resulting in constant concentrations or partial pressures of reactants and products. |
| Le Châtelier's principle | A principle stating that when a system at equilibrium is disturbed, the system shifts to counteract the disturbance and re-establish equilibrium. |
| Nernst equation | The equation E = E° − (RT/nF) ln Q that relates cell potential to standard cell potential and the reaction quotient under nonstandard conditions. |
| nonstandard conditions | Electrochemical conditions where concentrations of active species differ from 1 M, pressures differ from 1 atm, or temperature differs from 25°C. |
| reaction quotient | A value calculated using the same expression as the equilibrium constant but using current (non-equilibrium) concentrations or partial pressures. |
| spontaneous electron flow | The natural movement of electrons from the anode to the cathode in an electrochemical cell driven by the cell potential. |
| standard cell potential | The cell potential (E°) measured under standard conditions where all concentrations are 1 M, pressure is 1 atm, and temperature is 25°C. |
| Term | Definition |
|---|---|
| dispersal of matter | The spreading out of particles over a larger volume, allowing them greater freedom of movement. |
| entropy change | The difference in entropy between the final and initial states of a system during a chemical or physical process. |
| kinetic energy distribution | The range and spread of energy values among particles in a system, which broadens as temperature increases. |
| kinetic molecular theory | A model explaining the behavior of gases based on the motion of particles and the distribution of kinetic energy among them. |
| moles of gas-phase products | The quantity of gaseous substances produced in a reaction, used to compare entropy changes in gas-phase reactions. |
| moles of gas-phase reactants | The quantity of gaseous substances that react in a chemical reaction, used to compare entropy changes in gas-phase reactions. |
| phase change | A transition between states of matter, such as from solid to liquid or liquid to gas. |
| Term | Definition |
|---|---|
| charge | A fundamental property of matter measured in coulombs (C), related to current and time by the equation I = q/t. |
| charge flow | The movement of electric charge through a circuit, measured in coulombs and related to current and time. |
| current | The flow of electrical charge through a circuit, measured in amperes. |
| electrochemical cell | A device consisting of electrodes and electrolyte solutions where redox reactions occur, either spontaneously (galvanic) or non-spontaneously (electrolytic). |
| electrode | A conductor through which electric current enters or leaves an electrochemical cell. |
| electrons transferred | The number of electrons moving from a reducing agent to an oxidizing agent during a redox reaction. |
| electroplating | An electrochemical process in which a metal is deposited onto an electrode through the reduction of metal ions. |
| Faraday's laws | Fundamental principles relating the amount of chemical change in an electrochemical cell to the quantity of electric charge passed through it. |
| ionic species | Charged particles (ions) that participate in electrochemical reactions and carry charge in solution. |
| oxidation-reduction reaction | A chemical reaction involving the transfer of one or more electrons between chemical species, indicated by changes in oxidation numbers. |
| stoichiometry | The quantitative relationship between reactants and products in a balanced chemical equation that determines the rates of change of their concentrations. |
| Term | Definition |
|---|---|
| absolute entropies | The total entropy of a substance at a given temperature and pressure, measured relative to zero entropy at absolute zero. |
| entropy change | The difference in entropy between the final and initial states of a system during a chemical or physical process. |
| standard entropy change | The change in entropy for a chemical or physical process under standard conditions, calculated as the difference between the absolute entropies of products and reactants. |
| standard molar entropies | The absolute entropy of one mole of a substance under standard conditions, typically used to calculate entropy changes in reactions. |
| Term | Definition |
|---|---|
| enthalpy | The total heat content of a system; at constant pressure, the enthalpy change equals the thermal energy transferred to or from the surroundings during a chemical or physical process. |
| entropy | A measure of the disorder or randomness in a system, including the dispersal of dissolved particles and reorganization of solvent molecules during dissolution. |
| Gibbs free energy change | The change in Gibbs free energy (ΔG°) for a chemical or physical process, measured under standard conditions, that indicates whether a process is thermodynamically favored. |
| standard Gibbs free energy of formation | The Gibbs free energy change (ΔG°f) when one mole of a substance is formed from its elements in their standard states. |
| standard state | The reference condition for a substance: pure substances, solutions at 1.0 M concentration, or gases at 1.0 atm (or 1.0 bar) pressure. |
| temperature dependence | The relationship between temperature and whether a process is thermodynamically favored, determined by the signs and magnitudes of ΔH° and ΔS°. |
| thermodynamically favored | A reaction or process that has a negative Gibbs free energy (ΔG < 0) and is spontaneous under given conditions. |
| Term | Definition |
|---|---|
| activation energy | The minimum energy required for reactants to overcome the energy barrier and proceed to products in a chemical reaction. |
| equilibrium | The state in which the forward and reverse reaction rates are equal, resulting in constant concentrations or partial pressures of reactants and products. |
| kinetic control | A situation where a thermodynamically favored process does not proceed at a noticeable rate due to a high activation energy barrier. |
| kinetics | The study of the rate at which a chemical reaction occurs and the factors that influence this rate. |
| measurable rate | A reaction rate that is fast enough to be observed and quantified within a reasonable time frame. |
| thermodynamically favored | A reaction or process that has a negative Gibbs free energy (ΔG < 0) and is spontaneous under given conditions. |
| Term | Definition |
|---|---|
| equilibrium constant | A numerical value that expresses the ratio of products to reactants at equilibrium, indicating the extent to which a reaction proceeds. |
| RT (gas constant × temperature) | The product of the universal gas constant and absolute temperature; used in the relationship between K and ΔG°. |
| standard conditions | The reference conditions (typically 25°C, 1 M concentration, 1 atm pressure) under which ΔG° and K are evaluated. |
| standard Gibbs free energy change | The change in free energy under standard conditions; negative values indicate thermodynamically favored processes that favor products. |
| thermodynamically favored | A reaction or process that has a negative Gibbs free energy (ΔG < 0) and is spontaneous under given conditions. |
| Term | Definition |
|---|---|
| dissolution | The process by which a solute dissolves in a solvent to form a solution, involving the breaking of bonds or interactions in the solute and formation of new interactions with the solvent. |
| enthalpy | The total heat content of a system; at constant pressure, the enthalpy change equals the thermal energy transferred to or from the surroundings during a chemical or physical process. |
| entropy | A measure of the disorder or randomness in a system, including the dispersal of dissolved particles and reorganization of solvent molecules during dissolution. |
| Gibbs free energy change | The change in Gibbs free energy (ΔG°) for a chemical or physical process, measured under standard conditions, that indicates whether a process is thermodynamically favored. |
| intermolecular interactions | Forces between molecules, such as hydrogen bonding, dipole-dipole forces, and London dispersion forces, that affect the physical and chemical properties of substances. |
| salt | An ionic compound formed from the reaction of an acid and a base. |
| solubility | The maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature, typically expressed in moles per liter (molarity) or grams per 100 mL of solvent. |
| solvent | The substance, typically a liquid, in which a solute dissolves to form a solution. |
| Term | Definition |
|---|---|
| ATP to ADP conversion | The hydrolysis of adenosine triphosphate to adenosine diphosphate, a thermodynamically favorable reaction that releases energy to drive unfavorable biological processes. |
| common intermediates | Shared chemical species or compounds that participate in multiple reactions within a coupled reaction system. |
| coupled reactions | Two or more reactions that share common intermediates, where a thermodynamically favorable reaction is linked to drive a thermodynamically unfavorable reaction forward. |
| electrolytic cell | An electrochemical cell in which electrical energy is used to drive a non-spontaneous redox reaction. |
| external source of energy | Energy supplied from outside a system to drive a process that would not occur spontaneously, such as electrical energy or light. |
| photosynthesis | The process by which light energy is used to drive the thermodynamically unfavorable conversion of carbon dioxide and water into glucose. |
| standard Gibbs free energy change | The change in free energy under standard conditions; negative values indicate thermodynamically favored processes that favor products. |
| thermodynamically unfavored | A reaction that does not proceed spontaneously under standard conditions, resulting in a negative cell potential and positive Gibbs free energy change. |
| Term | Definition |
|---|---|
| anode | The electrode where oxidation occurs in an electrochemical cell. |
| cathode | The electrode where reduction occurs in an electrochemical cell. |
| current | The flow of electrical charge through a circuit, measured in amperes. |
| electrochemical cell | A device consisting of electrodes and electrolyte solutions where redox reactions occur, either spontaneously (galvanic) or non-spontaneously (electrolytic). |
| electrode | A conductor through which electric current enters or leaves an electrochemical cell. |
| electrode mass | The mass of an electrode, which can change during electrochemical reactions due to oxidation or reduction at the electrode surface. |
| electrolytic cell | An electrochemical cell in which electrical energy is used to drive a non-spontaneous redox reaction. |
| electron flow | The movement of electrons through the external circuit of an electrochemical cell from the anode to the cathode. |
| galvanic cell | An electrochemical cell in which a spontaneous redox reaction generates electrical current. |
| half-cells | Individual compartments of an electrochemical cell, each containing an electrode and electrolyte solution where a half-reaction occurs. |
| half-reaction | Separate equations showing either the oxidation process (loss of electrons) or the reduction process (gain of electrons) in a redox reaction. |
| ion flow | The movement of ions through the electrolyte and salt bridge to complete the circuit in an electrochemical cell. |
| oxidation | The loss of electrons by a substance in a redox reaction. |
| reduction | The gain of electrons by a substance in a redox reaction. |
| salt bridge | A tube containing an inert electrolyte that connects two half-cells and allows ion flow to maintain electrical neutrality. |
| thermodynamically favored | A reaction or process that has a negative Gibbs free energy (ΔG < 0) and is spontaneous under given conditions. |
| thermodynamically unfavored | A reaction that does not proceed spontaneously under standard conditions, resulting in a negative cell potential and positive Gibbs free energy change. |
| Term | Definition |
|---|---|
| electrochemical cell | A device consisting of electrodes and electrolyte solutions where redox reactions occur, either spontaneously (galvanic) or non-spontaneously (electrolytic). |
| half-reaction | Separate equations showing either the oxidation process (loss of electrons) or the reduction process (gain of electrons) in a redox reaction. |
| oxidation half-reaction | The half-reaction in which a species loses electrons. |
| oxidation-reduction reaction | A chemical reaction involving the transfer of one or more electrons between chemical species, indicated by changes in oxidation numbers. |
| reduction half-reaction | The half-reaction in which a species gains electrons. |
| standard cell potential | The cell potential (E°) measured under standard conditions where all concentrations are 1 M, pressure is 1 atm, and temperature is 25°C. |
| standard Gibbs free energy change | The change in free energy under standard conditions; negative values indicate thermodynamically favored processes that favor products. |
| standard reduction potential | The voltage associated with a reduction half-reaction under standard conditions, used to calculate the overall cell potential. |
| thermodynamically favored | A reaction or process that has a negative Gibbs free energy (ΔG < 0) and is spontaneous under given conditions. |
| thermodynamically unfavored | A reaction that does not proceed spontaneously under standard conditions, resulting in a negative cell potential and positive Gibbs free energy change. |