Creating ownDB!!!

[PhDstudent]

Hi everyone!! I'm a new member of The HSC Chemistry forum.I'm working with HSC Chemistry (version 5.1) and have some difficulties connecting with database!

I’ve created my ownDB file for certain species. I’ve put for certain temperature range ΔH, ΔS, and A, B, C constants. At the end I can’t get the same result calculated by hand and calculated by program. I suppose that the program doesn’t take account the data which have too small values (for example A, B, C constants that I’ve put -B and C have too small values and the program takes only A for calculations ). And because of this I got different ΔH, ΔG, ΔS especially in high temperatures. Could you please be so kind and give me some hints what to do? Or is it possible that I did something wrong?
I would appreciate to any help

THanks a lot!!!

[Eltee]

Without seeing the example, it's hard to specifically diagnose the problem. Round-off error (well, differences) in the Cp Coefficients is a possibility, as you point out.
Do you get identical results by hand and by HSC at 25C?
Do you get identical results if you use, in your hand calculation, the coefficient values as HSC stores them (however it rounds them off)?

Other factors that might be involved:

Is the assumed standard state the same? (i.e., 1 bar/25C, not 1 atm/25C).
Are there species involved in the reactions (not the new ones you created), for which the basic data differs slightly between that used in your hand calculation and that found in the HSC data base?

[PhDstudent]

First of all thank you for replay!!! I really appreciate it
The reaction is Formation of dimethyl ether from methanol. It has 3 species (MeOH, DME, H2O).At first I’ve tried to do calculation using the data from MainDB file and the results were different even at T=298K. I thought because of there is not exactly the same reference for all 3 species. Then created ownDB file and put data for all 3 species from the same book (Robert C. Reid, John M. Prausnitz, “The properties of Gases and Liquids” third edition) .After that I got the identical result only at T=298K.
I did calculation by hand and use only A (I assumed that B and C equal to 0) and got identical result by hand and by program.
But I realized that HSC program uses for Cp calculation the Kelley equation in this form.
Cp=A + B . 10-3 . T + C . 105 . T-2
Instead of this form
Cp=A + B . T - C .T-2
Meanwhile I use in my calculation well known equation Cp=A + B.T + C.T2

Now I have two more questions
Why the program uses the Kelley equation?
Why the Kelley equation has different form Cp=A + B . 10-3 . T + C . 105 . T-2 ?

Thank you beforehand!

[Eltee]

Now I have two more questions
Why the program uses the Kelley equation?
Why the Kelley equation has different form Cp=A + B . 10^-3 . T + C . 10^5 . T^-2 ?

It sounds like you've determined the cause of the discrepancies.

I don't work at Outotec... I'm just a user of the program. I can't say why that particular functional form was chosen for Cp. I, too, have Cp data using other functional formats and, when I want to add my data to HSC, I have to convert the curve to the HSC format.

[PhDstudent]

I’m very sorry that my question sounds as you mentioned . I really appreciate that you share your experience with new users of this forum.
I also converted Cp coefficient to HSC format but still I get different results in high temperatures.

Anyway thank you very much