Difference between KIN_DELTA and SAVE moles

[ciegolon]

Hi,

Sorry for this basic question,

I'm trying to understand is the difference between KIN_DELTA, defined as "moles of kinetic reactant that reacted during the current calculation" and SAVE moles, defined as "moles of kinetic reactant for a time step". I'm playing the Ex.9 and even though KIN_DELTA and SAVE moles (obtained via PUT, GET) have a definition that feels the same (to me, a beginner), the numbers are not the same.

Could anyone please explain this to me?

Thanks,

[dlparkhurst]

We are integrating the rate expressions over a time, say delta_t. The numerical integration method, either Runge Kutta (explicit) or CVODE (implicit) breaks the delta_t into sub time steps. So the rate and moles of reaction (SAVE moles) are evaluated multiple times over the course of the integration and the total amount of reaction over delta_t is calculated from these multiple rate estimates.

So, SAVE moles is encountered several or many times before the calculation is completed. The times at which is evaluated are determined internally. The final time when SAVE moles is executed may or may not be the time t + delta_t. Further, it may have been necessary to break the integration up in many smaller time steps to achieve the tolerance specified for the integration. All the SAVE moles executions are not too meaningful to you relative to the completed integration. The value of KIN_DELTA is the total moles of kinetic reaction over the delta_t interval. The average rate is KIN_DELTA / KIN_TIME.