1st layer (chemisorbed-like)
Layers 2+ (liquid-like)
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Real gas adsorption on a solid surface rarely stops at one molecular layer. The BET (Brunauer–Emmett–Teller) theory explains how, above roughly a third of the saturation pressure, additional layers begin stacking on top of the first before the surface is even fully covered. This simulator runs an actual kinetic birth–death process on a grid of independent surface sites — each site randomly gains or loses molecules at rates set by the relative pressure P/P₀ and the surface-affinity constant C — and renders the resulting stacks in 3D. The measured average coverage converges live to the closed-form BET isotherm equation, the same equation used industrially to measure the surface area of catalysts, activated carbon and porous materials from a single adsorption experiment.