# Chemical equilibrium A reaction reaches equilibrium when the forward and reverse rates match. Nothing stops — molecules keep converting in both directions — but the concentrations hold steady, which is why it is called dynamic. The position of that balance is fixed by the equilibrium constant K, and K is fixed in turn by the standard [[Gibbs_free_energy]] change of the reaction. ## Microsim — p5.js Sidecar: `Chemical_equilibrium.p5.js` · route leaf: `microsim/p5js/Chemical_equilibrium__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `kf slider` | forward rate constant | | `kr slider` | reverse rate constant | | `[r]` | reset to all reactant | *What to watch:* Set forward and reverse rate constants and watch the two concentrations converge. They stop changing while the arrows keep flowing — equilibrium is dynamic, not dead. ## Balance, not exhaustion The common misreading is that a reaction runs until something is used up. Most do not: they run until the [[Chemical_potential|potentials]] of reactants and products balance, and then sit there. Disturb the balance — add reactant, remove product, change temperature or pressure — and the system shifts to partially undo the disturbance, which is Le Chatelier's principle. Industrial chemistry lives on that shift: the [[Haber_process]] runs at high pressure precisely because squeezing a reaction that consumes gas molecules pushes it forward. ## Rate is a separate question K says where the balance sits, not how fast it gets there. [[Hydrogen]] and [[Oxygen]] have an enormous K for forming [[Water]] and will nonetheless coexist indefinitely without a spark, because the activation barrier is high. A catalyst lowers that barrier and speeds both directions equally — it changes arrival time, never destination. That distinction between thermodynamics and kinetics is the single most useful thing on this page, and it governs everything from [[Combustion]] to a [[Fuel_cell]]'s platinum. **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_potential]] · [[Combustion]] · [[Redox]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Chemical_equilibrium) : [Wikitube](https://en.wikitube.io/wiki/Chemical_equilibrium) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Hydrogen]], [[PORTAL_Oxygen]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*