01IUPAC · 2025
Loading STEMORIA content
Open a controlled gas inlet, set the feed, and explain the forced response and subsequent relaxation using Q/K, ΔᵣG, and the forward/reverse rate imbalance.
External control
gas feed
Stays fixed
Kc
Reveals response
Q/K + ΔᵣG + rates
Live scientific model
Observe → manipulate → measure → interpret → explain
Open molecular equilibrium laboratory
Operate the physical gas valve, watch the molecular population respond, then inspect the same state quantitatively. Controls are kept separate from evidence so the experiment stays readable.
Calculated concentration controls the representative population. Gas tint follows NO₂ concentration qualitatively and is not an absorbance calibration. Feed streamlines, molecular paths and staged bond-event cinema communicate reaction bookkeeping; they are not transition-state calculations or literal molecular dynamics.
Live causal chain
See why the reactor moves, not only which way.
External control
source term = 0
Composition test
Q/K ≈ 1
Thermodynamic sign
ΔᵣG ≈ 0
Kinetic evidence
rᶠ ≈ rʳ
Observed response
dynamic equilibrium
Kc is not in the chain as a changing variable because temperature remains fixed at 298.15 K. The chain compares the live composition-dependent Q with that fixed Kc.
Evidence drawer
Feed shading marks external forcing. After it ends, all later changes come from the reversible reaction itself. The graph and 3D population consume the same authoritative model state.
Timeline inspector
Inspect the experiment at any recorded model time
Hover, drag, or tap across the shared timeline. The crosshair reads the same authoritative history used by the reactor model; it does not interpolate a second hidden simulation.
Q/K
1.00
dynamic equilibrium
ΔᵣG
-2.75e-16 kJ/mol
near zero
[NO₂]
0.0155 M
product-side concentration
[N₂O₄]
0.0400 M
reactant-side concentration
r forward
0.00880 M s⁻¹*
teaching-scale
r reverse
0.00880 M s⁻¹*
teaching-scale
Pressure
1.357 atm
ideal-gas diagnostic
Feed
closed · no external source
unforced evolution
All panels use the same model-time axis. Feed shading marks the forced period; after the shading ends, changes come only from the reversible reaction. ΔᵣG is evaluated from RT ln(Q/K), and pressure is the ideal-gas diagnostic at the recorded composition.
Scientific notebook
A run is summarized only from the recorded model history. Saving does not alter the reactor or replay a hidden calculation.
Current run
Duration
0.0 s
Peak Q/K
1.00
Min Q/K
1.00
Peak P
1.357 atm
NO₂ feed
0.0 mmol
N₂O₄ feed
0.0 mmol
Final Q/K
1.00
Relaxation
not observed
Scientific model & limits
Valve open. The fixed 1.00 L teaching reactor includes a source term dC/dt = flow/V for the selected species. Moles and ideal-gas pressure therefore rise while feeding continues.
Valve closed. The source term is exactly zero. The same reversible mass-action model then evolves as a closed constant-volume reactor toward Q/K = 1.
3D view. Population follows calculated concentration. The manifold, incoming stream, tracked packet, and reaction flashes are representative visual cues rather than literal molecular dynamics.
Learning objective
Use Q and K to identify whether a reaction mixture has a forward tendency, reverse tendency, or is at equilibrium while recognizing that concentration changes do not change K at fixed temperature.
Both molecular directions remain active. Net change appears only when their rates differ.
NO₂ gives the gas its characteristic brown appearance, linking visible color to composition.
Q = [NO₂]²/[N₂O₄] converts composition into a quantitative comparison with K.
Scientific contract
Source-backed thermodynamics, pedagogically scaled kinetics, and representative 3D molecular motion are kept distinct.
Source anchored
Thermodynamics
Model boundaries are declared directly in the experiment.
Scaled
Teaching kinetics
Model boundaries are declared directly in the experiment.
Representative
3D motion
Model boundaries are declared directly in the experiment.
Scientific provenance