Reaction Conditions Page

Kinetiscope can be configured to simulate a range of different reaction conditions. The Reaction Conditions Page allows you to select among the available volume, pressure and temperature options, and to enter numeric values for system temperature, voltage and other parameters that influence rates.

The page looks like this:

To specify your settings, click on each of the five drop-down list boxes to see the available options. Use the mouse to select the option you want.

The content of the Temperature/Voltage/Simulus Values area changes according to the reaction conditions you select.

Not all combinations of temperature, volume and pressure are allowed (or physically meaningful). Options that are not applicable to the current reaction scheme will be visible in the drop-down lists but disabled.

The following tables summarize the available options:

Options for Single Reactor Reaction Schemes

Temperature Volume Pressure Electrode Potential External Stimulus
(1) variable variable constant not available not available
(2) variable constant variable not available not available
(3) variable constant constant not available not available
(4) programmed constant variable not available not available
(5) programmed variable constant not available not available
(6) programmed constant constant not available not available
(7) constant constant constant not available not available
(8) constant constant variable not available not available
(9) constant variable constant not available not available

The options intended for gas phase simulations are: 1, 2, 4, 5, 8 and 9. The options intended for condensed phase simulations are: 1, 3, 5, 6, 7, and 9.


Options for Compartmental Reaction Schemes

Temperature Volume Pressure Electrode Potential External Stimulus
(1) constant constant constant not available Off
(2) constant variable constant not available Off
(3) linearly programmed constant constant not available Off
(4) linearly programmed variable constant not available Off
(5) user-defined program constant constant not available Off
(6) user-defined program variable constant not available Off
(7) constant constant constant not available user-defined program
(8) constant variable constant not available user-defined program

Options for Three-Dimensional Reaction Schemes

Temperature Volume Pressure Electrode Potential External Stimulus
(1) constant constant constant Off Off
(2) constant variable constant Off Off
(3) linearly programmed constant constant Off Off
(4) linearly programmed variable constant Off Off
(5) user-defined program constant constant Off Off
(6) user-defined program variable constant Off Off
(7) constant constant constant Off user-defined program
(8) constant variable constant Off user-defined program
(9) constant constant constant user-defined program Off
(10) constant variable constant user-defined program Off

Volume Options

Volume is constant
When constant volume conditions are selected, the volume of the reacting system is held constant even though moles of species, temperature and pressure may change.

This option is intended for gas reactions and for reactions in dilute solution where the change in the system volume is negligible.

Volume is variable
When variable volume conditions are selected, the volume of the reacting system is allowed to change as the number of moles of each species changes.

This option is intended to be used for systems where the reactants and products are concentrated and the system volume undergoes significant change as the reactions proceed. The example simulations include demonstrations of how to use this option in a reaction scheme.

To use the variable volume option, you must enter on the Species Data Page molar densities for each species defined in the reaction scheme.

For single reactor reaction schemes only, the system must start as a single pure phase, but can evolve to include more than one phase. Because of the characteristics of a homogeneous simulator, only the total volume of those species declared to have the initial phase is calculated. The phase volume is updated and used to renormalize the concentrations of all species after each event in the simulation. Since the volume is only that of the initial phase, the concentrations of species formed in new phases during the course of a reaction (i.e. gas evolved as a solid reacts) will not be correct. No steps involving reactants in the new phases should be included in the reaction scheme, or the timebase of the simulation will not be meaningful. Kinetiscope does not check for this.

Pressure Options

Only single reactor reaction schemes allow variable pressure.

Pressure is constant
When constant pressure conditions are selected, the pressure of the system is constrained to remain constant, even though moles of species, temperature and volume may change. This is useful for gas and condensed phase simulations.
Pressure is variable
The variable pressure option is intended for gas phase reactions. The method by which the pressure is calculated depends on the accompanying temperature condition.
  • If temperature is constant or programmed, the system pressure is calculated from the ideal gas law:
    P  =  nRT
    V         		(1)
    where n is the number of moles, R is the gas constant, T is the temperature, and V is the volume. They are held constant for the calculation.
  • If temperature is variable, an adiabatic expansion/compression of the new volume Vnew to maintain constant volume V is carried out after each reaction event to calculate the new pressure Pnew using the expression:
    Pnew  =  Pold ( Vnew/ V )  Cp
    Cp - R         		(2)

    For an example, see the Example Simulation Thermal Decomposition of Ozone (I).

For each of the remaining options, you must also provide one or more numeric values in the Temperature/Voltage/Stimulus Values area at the bottom of the page. The appearance of that area changes according to the specific conditions you select.

Temperature Options

If your reaction scheme contains reaction steps or transfer steps with temperature-dependent rates, you must specify temperature conditions.

The following options are available:

Temperature is constant
For this setting the Temperature/Voltage/Stimulus Values area looks like this:

constant temperature

You must type in the Temperature data entry field the value to be used in the next simulation.
Temperature is variable
For this setting the Temperature/Voltage/Stimulus Values area looks like this:

variable temperature

You must enter values for the Initial Temperature and the Temperature Convergence Standard in the data entry fields.

Calculation of the new system temperature from the temperature-dependent thermochemistry is iterative, and this second parameter sets the maximum difference between two successive values. When the difference is less than the maximum the new temperature is saved. Convergence within 0.5 degrees is satisfactory for most cases. If there is any doubt, test the invariance of the result by halving this number. The default value is 0.1 degrees.

To use the variable temperature option, you also must enter thermochemical parameters on the Species Data Page for each species defined in the reaction scheme.

Temperature follows a linear profile
For this setting the Temperature/Voltage/Stimulus Values area looks like this:

linear temperature

You must specify values for T0 (the initial temperature), the Final Temperature, and b (the rate of temperature change in degrees per unit time). You also specify the Maximum Step Size, the largest temperature step that the simulation may take between iterations of the calculation loop.

Temperature follows a user-defined profile
For this setting the Temperature/Voltage/Stimulus Values area looks like this:

programmed temperature

When this condition is selected, a graph of the current temperature/time profile is displayed.

To modify the profile:
  • Click the Change Profile... push button.
    • This opens a Profile Editor Dialog that allows you to create, edit, import and export a temperature profile.

You also must enter in the Maximum Step Size data entry field the maximum temperature step that the simulation may take between iterations of the calculation loop.

Once defined, a temperature profile becomes part of the reaction file.

Voltage Options

If your reaction scheme contains electrochemical steps, you must specify voltage conditions.

The following voltage options are available:

Voltage is constant
You specify Constant Voltage and Constant Temperature values in the data entry fields.

Voltage follows a linear profile
For this setting the Temperature/Voltage/Stimulus Values area is similar to that for a linear temperature profile (see above). You must enter in the data entry fields values for V0 (the starting voltage), the Final Voltage, and b, the rate of voltage change in volts per unit time.

You also enter values ifor the Maximum Step Size of voltage steps that the simulation may take between iterations of the calculation, and the Temperature.

Voltage follows a user-defined profile
For this setting the Temperature/Voltage/Stimulus Values area is similar to that for a user-defined temperature profile (see above), displaying a graph of the current voltage/time profile.

To modify the profile:
  • Click the Change Profile... push button.
    • This opens a Profile Editor Dialog that allows you to create, edit, import and export a profile.

    You also enter values for the Maximum Step Size of voltage steps that the simulation may take between iterations of the calculation, and the Temperature.

    Once defined, a voltage profile becomes part of the reaction file.

You must use the Temperature is constant setting when any voltage option is selected. Kinetiscope will automatically set the constant temperature conditions when you select one of the voltage options.

In the default Voltage is off state, the voltage value is implicitly set to be zero.

External Stimulus Option

This setting allows you to control rates for reaction steps and transfer steps that you have designated to depend on the value of an external stimulus. The rate constant of such a step is directly proportional to the value of the external stimulus at the current elapsed time.

The magnitude of the external stimulus can vary with time in a user-defined manner. This facilitates the construction of reaction systems where external events influence the kinetics; for example, calculating drug concentrations upon multiple administrations of a drug dose, simulating chemistry stimulated by pulsed radiation, or modeing time-dependent photolysis as in photochemical smog.

In the default External stimulus is off state, the external stimulus value is set to be zero, which in effect deactivates any reaction steps that depend on its value.

To activate an external stimulus, set this option to

External Stimulus follows a user-defined profile

For this setting the Temperature/Voltage/Stimulus Values area appears similar to that for a user-defined temperature profile, and displays a graph of the current external stimulus/time profile.

To modify the profile:
  • Click the Change Profile... push button.
    • This opens a Profile Editor Dialog that allows you to create, edit, import and export a profile.

You also enter values for the Maximum Step Size of stimulus steps that the simulation may take between iterations of the calculation loop, and the Temperature.

Once defined, an external stimulus profile becomes part of the reaction file.