Battery knowledge · Electrochemistry fundamentals
Nernst equation
The relation between an electrode’s potential and the concentrations, or activities, of the species in its half-reaction. It explains why open-circuit voltage changes with state of charge and temperature. [1]
- Relationship
- E = E° − (RT/nF)·ln Q
Example
Change a reaction quotient by a decade
At 298.15 K with n = 1, increasing the dimensionless reaction quotient from 1 to 10 lowers E by about 59.2 mV. Use activities or a justified concentration approximation.
Explore the graph
The logarithm of the reaction quotient changes equilibrium potential; reference electrodes set the voltage zero.
A tenfold increase in Q shifts E by −59.16 mV at 25 °C for n = 1.
E − E° = −(RT/nF) ln Q; E(vs SHE) ≈ E(vs Li/Li⁺) − 3.04 V
Illustrative model. Q is dimensionless activity quotient, not electrical charge. The −3.04 V reference offset is an approximate conventional value; it is not recomputed with temperature.
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
- Nernst equation
IUPAC Gold Book · 2025
Technical reference · Equilibrium potential as a function of activities; distinguishes activities from concentration approximations.
Further reading on this topic
These sources provide broader context; they are not presented as citations for every statement in this entry.
- Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing
IUPAC · 2011
Topic background · Physical-chemistry notation, thermodynamics, electrochemistry and transport quantities.