Battery knowledge · Electrochemistry fundamentals
Gibbs free energy
The maximum useful work a reaction can deliver at constant temperature and pressure. For a cell it equals the charge transferred times the cell voltage, with a negative sign, which ties the thermodynamics of the materials to the voltage on the terminals. [1]
- Abbreviation
- ΔG
- Unit
- kJ/mol
- Relationship
- ΔG = −nFE
Example
Convert voltage to molar free energy
For a one-electron reaction with equilibrium voltage 3.0 V, ΔG = −nFE is approximately −289 kJ/mol. The sign refers to the reaction direction and the equilibrium electrical work.
Explore the graph
A spontaneous forward cell reaction has negative Gibbs energy and positive equilibrium voltage under this convention.
At 3.7 V, ΔG = -357 kJ/mol reaction for n = 1.
ΔG = −nFE
Illustrative model. Equilibrium relation at fixed temperature and pressure. No reaction chemistry, activity model or loaded voltage is calculated.
Use in Lemonergy
Connect reaction sites and transport paths.
This is a reference concept. No executable Lemonergy block has been verified for this term.
References & further reading
Technical references
- Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing
IUPAC · 2011
Technical reference · Physical-chemistry notation, thermodynamics, electrochemistry and transport quantities.