Example: Reaction at Quasi-Equilibrium
The following example shows how REX deals with reactions that are assumed as equilibriated.
Consider a reversible reaction R1 that involves the compounds A and B that will be considered as being at equilibrium; and a second reaction R2 that produces C from B:
After entering the compounds and the reactions, R1 should be selected as a Quasi-Equilibrium reaction in the Reactions node:
In the Kinetics node, both the forward as well as the reverse directions must be included for every quasi-equilibrium reaction.
After entering some values for the kinetics parameters, and performing the Initialize Orders action in the Parameters node, a snapshot of the Parameters node is shown below:
Next, an experimental set is defined where the initial contents are: A = 1 gmol, B = 0 gmol, C = 0.001 gmol:
After running the project with the Simulate Only solution option, the profiles node shows:
As it can be seen, the initial concentration of C has exactly the same initial value entered in the experimental set, but for the compounds A and B the initial values are not the same ones entered by the user in the experimental set.
This change in the initial concentration is done by REX, by using the user provided initial values and then finding their values at equilibrium. The subsequent concentrations of A and B will also satisfy the equilibrium constraint.
Note:
You should be aware that when dealing with an equilibriated reaction, the values of the preexponential and activation energy for the forward and reverse directions are not individually meaningful: what has real significance is the ratio between the forward and reverse preexponentials, and the difference between their related activation energies, as they define the value of the equilibrium constant.
Thus, the same results can be obtained in this example if you multiply the preexponential values of both direction of R1 by a nonzero number.
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Consider a reversible reaction R1 that involves the compounds A and B that will be considered as being at equilibrium; and a second reaction R2 that produces C from B:
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In the Kinetics node, both the forward as well as the reverse directions must be included for every quasi-equilibrium reaction.
After entering some values for the kinetics parameters, and performing the Initialize Orders action in the Parameters node, a snapshot of the Parameters node is shown below:
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Next, an experimental set is defined where the initial contents are: A = 1 gmol, B = 0 gmol, C = 0.001 gmol:
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|---|
After running the project with the Simulate Only solution option, the profiles node shows:
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|---|
As it can be seen, the initial concentration of C has exactly the same initial value entered in the experimental set, but for the compounds A and B the initial values are not the same ones entered by the user in the experimental set.
This change in the initial concentration is done by REX, by using the user provided initial values and then finding their values at equilibrium. The subsequent concentrations of A and B will also satisfy the equilibrium constraint.
Note:
You should be aware that when dealing with an equilibriated reaction, the values of the preexponential and activation energy for the forward and reverse directions are not individually meaningful: what has real significance is the ratio between the forward and reverse preexponentials, and the difference between their related activation energies, as they define the value of the equilibrium constant.
Thus, the same results can be obtained in this example if you multiply the preexponential values of both direction of R1 by a nonzero number.
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