Glossary
Ampere (Amp)
The SI unit of electric current, defined as one Coulomb of charge per second (C/s).
Example:
A 15 Amp current means 15 Coulombs of charge are flowing through the circuit every second.
Anode
The electrode in an electrochemical cell where oxidation occurs.
Example:
In a car battery, the lead electrode where lead is oxidized to lead(II) sulfate acts as the anode.
Cathode
The electrode in an electrochemical cell where reduction occurs.
Example:
In a car battery, the lead(IV) oxide electrode where lead(IV) is reduced to lead(II) sulfate acts as the cathode.
Cell Potential (E_cell)
The potential difference between the two half-cells in an electrochemical cell, indicating the driving force of the reaction. A negative E_cell indicates a nonspontaneous reaction.
Example:
If a reaction has an E_cell of -0.50 V, it means you need at least 0.50 V of external power to make it happen.
Coulomb
The SI unit of electric charge, representing the amount of charge transported by a constant current of one ampere in one second.
Example:
If a lightning bolt carries 10 Coulombs of charge, that's a significant amount of electrical energy.
Dimensional Analysis
A problem-solving method that uses the cancellation of units to convert between different units or to check the consistency of equations.
Example:
When converting grams to moles to atoms, dimensional analysis helps ensure you're multiplying and dividing by the correct conversion factors.
Electrolytic cells
Electrochemical cells that use an external power source to drive nonspontaneous redox reactions.
Example:
Electroplating a metal, like coating a cheap ring with gold, is done using an electrolytic cell.
Faraday's Constant
The charge carried by one mole of electrons, approximately 96,485 Coulombs per mole of electrons.
Example:
When calculating the mass of copper deposited during electrolysis, you'll use Faraday's Constant to convert between moles of electrons and total charge.
Faraday's Law
A law stating that the amount of substance produced or consumed at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the cell.
Example:
Using Faraday's Law, you can calculate exactly how much aluminum metal can be produced from a given amount of electrical current in an industrial smelter.
Galvanic cells (Voltaic cells)
Electrochemical cells that generate electrical energy from spontaneous redox reactions.
Example:
A common AA battery is a type of galvanic cell that spontaneously produces electricity to power your remote control.
Nonspontaneous redox reactions
Chemical reactions that require a continuous input of energy to proceed, as they do not occur naturally.
Example:
Charging a phone battery involves a nonspontaneous redox reaction where electrical energy forces the reverse of the discharge reaction.
Oxidation
A chemical process involving the loss of electrons, an increase in oxidation state, or the gain of oxygen.
Example:
When iron rusts, it undergoes oxidation as it loses electrons to oxygen, forming iron oxides.
Reduction
A chemical process involving the gain of electrons, a decrease in oxidation state, or the loss of oxygen.
Example:
In a photographic film, silver ions gain electrons to form solid silver, a classic example of reduction.
Salt bridge
A component of an electrochemical cell that connects the two half-cells and allows the flow of ions to maintain electrical neutrality.
Example:
Without a salt bridge, the charge imbalance in an electrochemical cell would quickly stop the reaction.
Standard Cell Potential (E°)
The cell potential measured under standard conditions (1 M concentration for solutions, 1 atm pressure for gases, 25°C).
Example:
A positive E° for a reaction indicates that it is spontaneous under standard conditions.
Standard Free Energy Change (ΔG°)
The change in Gibbs free energy for a reaction occurring under standard conditions, indicating the maximum amount of non-PV work that can be extracted from a spontaneous process.
Example:
A negative ΔG° value confirms that a reaction is spontaneous and can do useful work.
Standard Hydrogen Electrode (SHE)
A reference electrode used to measure standard electrode potentials, defined as having a standard reduction potential of 0.00 V.
Example:
The potential of any half-reaction is measured relative to the Standard Hydrogen Electrode.