# Chemical potential Chemical potential is the [[Gibbs_free_energy]] change per mole of a substance added — how much a system's free energy rises when one more particle of that species arrives. Matter flows from high chemical potential to low, exactly as heat flows from hot to cold, and stops when the potentials are equal. It is the quantity that makes [[Diffusion]], phase change, and reaction all one subject. ## Microsim — p5.js Sidecar: `Chemical_potential.p5.js` · route leaf: `microsim/p5js/Chemical_potential__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `μ° left / right` | standard potential of each compartment | | `[space]` | open or close the barrier | | `[r]` | reset to an imbalance | *What to watch:* Two compartments with different particle counts. Release the barrier and net flow runs down the potential difference, slowing to nothing as the two sides equalise — not when the counts match, but when μ does. ## Not concentration The common mistake is to treat chemical potential as a synonym for concentration. It is not: it also carries temperature, pressure, and the interactions between species. Two solutions at the same concentration can have different potentials, and matter will move between them. This is why osmosis pulls [[Water]] across a membrane toward the *saltier* side — the water's own potential is lower there — and why [[Properties_of_water|water activity]] rather than water content governs whether food spoils. ## Equality is equilibrium Every equilibrium on this spine is a statement about equal potentials. A [[Phase_diagram]] boundary is where two phases share one; a [[Chemical_equilibrium]] is where the weighted potentials of reactants and products balance; a [[Galvanic_cell]] at rest has its electrochemical potentials matched across the electrodes. In [[Two-phase_flow]] and in a [[Porous_medium]] the same gradient drives transport, and in [[Electrochemistry]] it is the electrochemical potential — chemical plus electrical — that decides which way ions go. **Reads with:** *Thermodynamics and Chemistry, 2nd ed. (Howard DeVoe, 2020)* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/thermodynamics-and-chemistry) · [download](https://www2.chem.umd.edu/thermobook/downloads.htm) · CC BY 4.0. Section 6 of the [[PORTAL_Thury_Hydrodynamics_Apex_Spine|Apex Spine]] book shelf. **On the spine:** [[Gibbs_free_energy]] · [[Chemical_equilibrium]] · [[Diffusion]] · [[Phase_diagram]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Chemical_potential) : [Wikitube](https://en.wikitube.io/wiki/Chemical_potential) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Physics]], [[PORTAL_Energy]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*