Note: In order to model
reactants, you must have the RT Module. If you are using the CT Module,
you can model decay, but cannot model any reactants.
GoldSim was designed to simulate first-order decay reactions. Note, however, that by defining the decay rate as a function of concentration(s), higher order reactions can also be represented.
For example, suppose you wanted to simulate the following reaction within GoldSim:
A ⇒ B
in which the reaction was second order:
d[A]/ dt = -k [A]2
where [A] is the mole concentration of A in the Cell of interest and k is the second order rate constant, with units of [(mole/m3)-1 yr-1]. First, of course, you would specify that B was a daughter of A. How then, would you represent the second order reaction rate?
In this case, we could rewrite the rate law as:
d[A]/dt = -{k cA / MWA} [A] = -k' [A]
where cA is the mass concentration, and MWA is the molecular weight. k' then represents a “pseudo first-order” rate constant. Specifying the "pseudo first-order" decay rate for A as the function “(k) (MWA)/AA” has the effect of simulating the second-order rate law.
Note that defining the decay rate as a function of the concentration creates a recursive model (since the dissolved concentration is a function of the decay rate, and the decay rate is a function of the dissolved concentration). Hence, when you do this, you must utilize a previous value element.
Note: In order to model
reactants, you must have the RT Module. If you are using the CT Module,
you can model decay, but cannot model any reactants.