Entropy Production & Affinity
Non-equilibrium Steady States · Onsager Relations
Network Parameters
Reaction Rate k₁ (A→B):
2.0
Back Rate k₋₁ (B→A):
0.5
Rate k₂ (B→C):
1.5
Back Rate k₋₂ (C→B):
0.3
Rate k₃ (C→A):
1.0
Back Rate k₋₃ (A→C):
0.8
—
Affinity A (kT)
—
σ (entropy prod)
—
Net cycle flux J
—
Equil. (A=0?)
Affinity:
A = ln(k₁k₂k₃/k₋₁k₋₂k₋₃) (Schnakenberg)
Entropy production:
σ = J·A ≥ 0
At equilibrium (A=0): detailed balance holds, no net flux. Away from equilibrium: nonzero affinity drives persistent cycling. Onsager: σ = Σ Jᵢ·Aᵢ, minimum entropy production at steady state.