CW%APG.PH.UCL.AC.UK@pucc.PRINCETON.EDU (04/05/91)
Hi,
In the equation library ROM the specific heat for atomic oxygen
is listed as .92 J/(g*K). A reliable source ( supposedly a man
from HP in Switzerland) phoned me up after I had made some enquiries
as to the meaning of this number, and told me it was the specific
heat at constant pressure (i.e. Cp). I have just found out
that in the J.A.N.A.F. tables the specific heat at constant
pressure for atomic oxygen is listed as 22.74 J/K/mol. Lets
do some conversions....
for O 22.74 J/K/mol is equivalent to 1.421 J/(g*K).
Hmm me thinks something not right,
for O 0.92 J/K/mol is equivalent to 14.72 J/(K*mol).
This is equivalent to a 35% discrepancy. This
is rather fundamental to me since I do Atmospheric modelling
and one of the important parameters is the specific heat
capacity of atomic oxygen at constant pressure.
So could a nice kind HP person reading this possibly put me
right? I would be very grateful.
Thanks
Conrad
P.S. The J.A.N.A.F. tables come from the National Bureau of standardswaterman@engg.ucalgary.ca (jason waterman) (04/06/91)
Hi there, In a previous article, Conrad wrote: > Hi, > In the equation library ROM the specific heat for atomic oxygen > is listed as .92 J/(g*K). A reliable source ( supposedly a man > from HP in Switzerland) phoned me up after I had made some enquiries > as to the meaning of this number, and told me it was the specific > heat at constant pressure (i.e. Cp). I have just found out > that in the J.A.N.A.F. tables the specific heat at constant > pressure for atomic oxygen is listed as 22.74 J/K/mol. Lets > do some conversions.... > > for O 22.74 J/K/mol is equivalent to 1.421 J/(g*K). > > Hmm me thinks something not right, > > for O 0.92 J/K/mol is equivalent to 14.72 J/(K*mol). > > This is equivalent to a 35% discrepancy. This > is rather fundamental to me since I do Atmospheric modelling > and one of the important parameters is the specific heat > capacity of atomic oxygen at constant pressure. > > So could a nice kind HP person reading this possibly put me > right? I would be very grateful. > > Thanks > > Conrad > > P.S. The J.A.N.A.F. tables come from the National Bureau of standards I'm not from HP, but I did some checking and found the same value of .92 J/(g*K) in two sources, my thermodynamics text and the CRC handbook of Chemistry and physics. I also found that this was the value of Cpo which is defined as the zero-pressure constant-pressure specific heat. The values I found were for Oxygen Gas O2, so this could be the problem. The difference could also be due to the fact that the 0.92 J/(g*K) is for zero-pressure and further calculations are necessary to obtain the Cp value for the pressure you are working at. Maybe someone more familiar with thermodynamics could elaborate, since I'm not finished the course yet. Also, I believe that there is an error in the units you gave for your value of specific heat of Oxygen. You gave the value of 22.74 J/K/mol. I think that it should be 22.74 J/(mol*K). Hope this helps. P.S. > for O 0.92 J/K/mol is equivalent to 14.72 J/(K*mol). ^? ^? I'm wondering how you managed that conversion. Shouldn't it be 0.92 J/(g*K)? ------------------------------------------------------------------------------- Jason Waterman The University of Calgary Calgary, Alberta, Canada Email: waterman@engg.ucalgary.ca -------------------------------------------------------------------------------
Dan_Ciarniello@cc.sfu.ca (04/08/91)
>> Hi, >> In the equation library ROM the specific heat for atomic oxygen >> is listed as .92 J/(g*K). A reliable source ( supposedly a man >> from HP in Switzerland) phoned me up after I had made some enquiries >> as to the meaning of this number, and told me it was the specific >> heat at constant pressure (i.e. Cp). I have just found out >> that in the J.A.N.A.F. tables the specific heat at constant >> pressure for atomic oxygen is listed as 22.74 J/K/mol. Lets >> do some conversions.... >> >> for O 22.74 J/K/mol is equivalent to 1.421 J/(g*K). >> >> Hmm me thinks something not right, >> >> for O 0.92 J/K/mol is equivalent to 14.72 J/(K*mol). >> >> This is equivalent to a 35% discrepancy. This >> is rather fundamental to me since I do Atmospheric modelling >> and one of the important parameters is the specific heat >> capacity of atomic oxygen at constant pressure. >> >> So could a nice kind HP person reading this possibly put me >> right? I would be very grateful. >> >> Thanks >> >> Conrad >> >> P.S. The J.A.N.A.F. tables come from the National Bureau of >standards > > >I'm not from HP, but I did some checking and found the same value of >.92 J/(g*K) in two sources, my thermodynamics text and the CRC handbook of >Chemistry and physics. I also found that this was the value of Cpo which is >defined as the zero-pressure constant-pressure specific heat. The values I >found were for Oxygen Gas O2, so this could be the problem. The difference >could also be due to the fact that the 0.92 J/(g*K) is for zero-pressure and >further calculations are necessary to obtain the Cp value for the pressure >you are working at. Maybe someone more familiar with thermodynamics could >elaborate, since I'm not finished the course yet. Also, I believe that >there is an error in the units you gave for your value of specific heat of >Oxygen. You gave the value of 22.74 J/K/mol. I think that it should be >22.74 J/(mol*K). > >Hope this helps. > >P.S. > >> for O 0.92 J/K/mol is equivalent to 14.72 J/(K*mol). > ^? ^? > >I'm wondering how you managed that conversion. Shouldn't it be 0.92 J/(g*K)? > > >----------------------------------------------------------------------------- >-- >Jason Waterman >The University of Calgary >Calgary, Alberta, Canada >Email: waterman@engg.ucalgary.ca >----------------------------------------------------------------------------- I found the same result as John did in the CRC handbook (although my copy gives a value of 0.219 cal/(g*K) which is equivalent to 0.92 J/(g*K)). However, I figure that John must be an engineer when he says that that is the value at zero-pressure ( :) ). The value given is at 25C and 1 atmosphere (which I believe some engineering disciplines refer to as 0 pressure). I suspect that the discrepancy between the CRC (and HP) value and the J.A.N.A.F. value is because the CRC value is for molecular oxygen (O2) while the J.A.N.A.F. value is for atomic oxygen (O). Conrad, I suspect that the value for O2 would be more relevant for doing atmospheric modelling since there is little if any free O in the atmosphere. Dan Ciarniello Capilano College North Vancouver, B. C.
Dan_Ciarniello@cc.sfu.ca (04/09/91)
Apologies to Jason Waterman for referring to him as John in my previous posting. Dan Ciarniello Capilano College North Vancouver, B. C.