Sciencemadness Discussion Board

heat capacity of Sorguyl

BASF - 13-5-2003 at 00:39

I´m looking for the value for Cv or Cp for Tetranitroglycoluril, which i need for the calculation of detonation pressure.
I did a search on NIST, but only the value for HMX was available.

It´s a pity i forgort my physics-book at home......wasn´t there a method to estimate heat capacities of solids?
I remember something vaguely like it was 2,5 J/mol K or something like this which was said could be used as a rough estimation-value.

I would be grateful for any info on this.

HLR

I am a fish - 13-5-2003 at 04:29

You're probably thinking of the Dulong-Petit formula...

C = 3NR

Where...

C = heat capacity
N = Moles of atoms
R = Ideal Gas Constant (8.3145 J / K)

Remember that this is only a classical approximation and may be wildly inaccurate in certain cases (e.g. diamond).

If you require something better, look up 'Debye Model'.

BASF - 13-5-2003 at 07:33

Thanks a lot !

- Thats it. I know rough means really rough in this case......thanks for the hint on the "debye-model", i´ll try that.

Microtek - 15-5-2003 at 07:18

I think you should use the tabulated value of a somewhat similar material. And a heat capacity of 25 J/K*mol doesn't seem right at all when talking about solids ( for HMX the actual value is about 290 J/K*mol ), so maybe C = 3NR goes for gases ?

I am a fish - 16-5-2003 at 10:16

Quote:
Originally posted by Microtek
I think you should use the tabulated value of a somewhat similar material. And a heat capacity of 25 J/K*mol doesn't seem right at all when talking about solids ( for HMX the actual value is about 290 J/K*mol ), so maybe C = 3NR goes for gases ?


It's for solids. It just doesn't work in this case.

Dany - 22-9-2013 at 03:12

The heat capacity at constant pressure Cp of Sorguyl (TNGU) is 67.8 cal mol−1 K−1 (or 283.67 J mol-1 K-1) (@ T= 300 K ). This value is calculated theoretically using Ab initio quantum chemical method. in the attached file you will find other interesting properties for many other energetic materials (42 compounds) such as gaseous enthalpy of formation, Cp and S0 (entropie).

Dany.

Attachment: Ab initio quantum chemical predictions.pdf (181kB)
This file has been downloaded 610 times

Dornier 335A - 22-9-2013 at 22:25

I fail to see why the heat capacity of an explosive is necessary for calculating its detonation pressure. Could you explain?

watson.fawkes - 24-9-2013 at 03:47

Quote: Originally posted by Dornier 335A  
heat capacity of an explosive is necessary for calculating its detonation pressure
Energy liberated has to go somewhere. The more it goes into heating the solid material prior to reaction, the less is available to other modes, such as the energy of a pressurized gas.