Glossary
Ecell
The cell potential under non-standard conditions, which varies with temperature and the actual concentrations of reactants and products.
Example:
If you dilute the reactant concentrations in a battery, the Ecell will likely decrease, making the battery less powerful.
Equilibrium
In an electrochemical cell, this is the state where the net flow of electrons ceases, meaning the forward and reverse reaction rates are equal and Ecell = 0.
Example:
When your phone battery dies, it means the electrochemical reactions inside have reached equilibrium, and there's no longer a potential difference to drive current.
Equilibrium Constant (K)
The ratio of product concentrations to reactant concentrations at equilibrium, indicating the extent to which a reaction proceeds to completion.
Example:
A very large Equilibrium Constant for a redox reaction indicates that the reaction strongly favors product formation at equilibrium.
E°cell
The standard cell potential, which is the cell voltage measured under standard conditions (298.15 K, 1 atm pressure for gases, and 1 M concentrations for solutions).
Example:
For a standard copper-zinc cell, the E°cell is +1.10 V, indicating a strong spontaneous reaction under ideal conditions.
F (Faraday's constant)
The charge carried by one mole of electrons, approximately 96,485 coulombs per mole of electrons, crucial for relating electrical charge to chemical change.
Example:
Faraday's constant is essential for converting between electrical charge and moles of electrons in electrochemistry calculations.
Galvanic cell
An electrochemical cell that generates electrical energy from a spontaneous redox (reduction-oxidation) reaction.
Example:
A common AA battery is a type of galvanic cell that converts chemical energy into electrical energy to power your remote.
Gibbs Free Energy (ΔG)
A thermodynamic quantity that measures the maximum reversible work that may be performed by a thermodynamic system at constant temperature and pressure; a negative ΔG indicates spontaneity.
Example:
For a spontaneous electrochemical cell, the Gibbs Free Energy change will be negative, indicating that the reaction can do work.
Nernst Equation
An equation that quantifies how non-standard conditions (temperature and concentrations) affect the cell potential (Ecell) relative to the standard cell potential (E°cell).
Example:
Using the Nernst Equation, you can predict how much the voltage of a battery will drop as its reactant concentrations decrease during discharge.
R (Gas Constant)
A fundamental physical constant (8.314 J/mol·K) used in thermodynamic equations, including the Nernst equation, to relate energy to temperature and moles.
Example:
In the ideal gas law, PV=nRT, R helps us relate pressure, volume, moles, and temperature for gases.
Reaction Quotient (Q)
A measure of the relative amounts of products and reactants present in a reaction at any given time, used to predict the direction a reaction will shift to reach equilibrium.
Example:
If the Reaction Quotient for a cell is less than 1, it means there are more reactants than products, and the cell potential will be higher than standard.
Standard Conditions
A set of reference conditions for thermodynamic measurements, typically 298.15 K (25°C), 1 atm pressure for gases, and 1 M concentration for solutions.
Example:
When you see E°cell, it means the cell potential was measured under Standard Conditions.
T (Temperature in Kelvin)
The absolute temperature scale used in thermodynamic calculations, where 0 K represents absolute zero and is required for equations like the Nernst equation.
Example:
To use the Nernst equation, you must convert Celsius temperatures to Temperature in Kelvin by adding 273.15.
n (moles of electrons transferred)
The stoichiometric number of moles of electrons that are exchanged in the balanced overall redox reaction of an electrochemical cell.
Example:
In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, the value of n is 2 because two electrons are transferred from zinc to copper.