Basic Equilibrium  

Systems modeling is a natural for showing equilibrium. This model demonstrates three different ways in which models can be built to show equilibrium in the generic reaction A yields B. The second version (Reactant A2 and Product B2) is the format most frequently used.

THE MODELS
Vensim Version STELLA Version

[Diagram Level | Equations Level | Graphs ]



Product_B(t) = Product_B(t - dt) + (rate_B_appears - rate_B_disappears) * dt
INIT Product_B = 0

INFLOWS:
rate_B_appears = rate_A_decomposes
OUTFLOWS:
rate_B_disappears = Product_B*reverse_rate_constant
Product_B2(t) = Product_B2(t - dt) + (rate_forward - rate_reverse) * dt
INIT Product_B2 = 0

INFLOWS:
rate_forward = forward_rate_constant*Reactant_A2
OUTFLOWS:
rate_reverse = reverse_rate_constant*Product_B2
Product_B3(t) = Product_B3(t - dt) + (rate_reaction) * dt
INIT Product_B3 = 0

INFLOWS:
rate_reaction = forward_rate_constant*Reactant_A3-reverse_rate_constant*Product_B3
Reactant_A(t) = Reactant_A(t - dt) + (rate_A_appears - rate_A_decomposes) * dt
INIT Reactant_A = 100

INFLOWS:
rate_A_appears = rate_B_disappears
OUTFLOWS:
rate_A_decomposes = Reactant_A*forward_rate_constant
Reactant_A2(t) = Reactant_A2(t - dt) + (rate_reverse - rate_forward) * dt
INIT Reactant_A2 = 100

INFLOWS:
rate_reverse = reverse_rate_constant*Product_B2
OUTFLOWS:
rate_forward = forward_rate_constant*Reactant_A2
Reactant_A3(t) = Reactant_A3(t - dt) + (- rate_reaction) * dt
INIT Reactant_A3 = 100

OUTFLOWS:
rate_reaction = forward_rate_constant*Reactant_A3-reverse_rate_constant*Product_B3
forward_rate_constant = .1
keq = forward_rate_constant/reverse_rate_constant
reverse_rate_constant = .05


Time Specs
Range: 0-50 , dT = 0.25 , Integration Method = Euler


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