SDB - Thermo2
Navigation: User Guide ➔ Species Properties ($SDB) ➔ Thermo2 Tab
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Thermo2 Tab
This tab page displays the following thermodynamic properties of ALL species in the project:
Entropy (Sf@T)
This is the absolute entropy defined by the Third Law so that Sf(0°K) = 0.
Gibbs Free Energy (Gf)
This is equal to [math]\displaystyle{ H_f - TS_f }[/math].
Gibbs Energy of Formation (DeltaGf)
[math]\displaystyle{ \Delta G_f }[/math] for a species is the difference [math]\displaystyle{ G_f(T, p) - \Sigma G^0_f(e) }[/math] where the sum is over the elements forming the species at standard conditions. Since the heat of formation [math]\displaystyle{ H^0_f = 0 }[/math] for elements at standard conditions, only the entropy contributes so the correction is [math]\displaystyle{ T\Sigma S^0(e) }[/math] This depends on both temperature and (in the case of gases) pressure; the values displayed are for [math]\displaystyle{ T, \,p }[/math] specified by $SDB.T and $SDB.P. The results are for pure species so there is no compositional dependence on $SDB.SoluteMF which is not displayed on the Thermo2 tab.
For example, in electrolysis of water, it represents the theoretical minimum energy to dissociate to the components H2 and O2, at standard conditions 237kJ/mol. Heat must be added to overcome the change in entropy, so in practice the practical limit is 286 kJ/mol, which is the standard heat of formation.
Numerically, [math]\displaystyle{ \Delta G_f = \mu }[/math], the chemical potential or partial molar free energy for the pure species. For pressure 1atm, the value is the standard chemical potential [math]\displaystyle{ \mu^0(T) }[/math] though for most solid and liquid species there is no pressure dependence. For species with charge [math]\displaystyle{ n }[/math] (which may be positive or negative) there is an additional correction [math]\displaystyle{ nS^0(\rm{H}_2(g))/2 }[/math]. The reference is the H+ ion, for which the potential is zero, and hydrogen gas: effectively, the contribution of the charge comes from a reaction H+ + e- <=> 1/2 H2(g)
At standard conditions, these values [math]\displaystyle{ \Delta G^0_f }[/math] should be close to those found in sources like the NBS tables See the comparison below. The NBS table has data for Gibbsite as Al2O3.3H2O; if we represent this as Al[OH]3, then the SysCAD value is one half of the NBS value.
Heating Values
This is the energy released if the compound is fully combusted with O2. The higher value is if the product contains liquid water while the lower value is if the product contains steam.
Entropy at 25°C (S25)
This is independent of the temperature setting at the top. (If the species has missing H25 data in the species database, then it will be marked with * and assumed a S value of 0 at 0°C.)
Temperature Limits
The lower (LoT) and upper (HiT) temperature limits for valid Cp data of individual compounds.
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- The Species Property Data shown here is given for a temperature of 25°C and a pressure of 101.325 kPa. These are standard or reference conditions. There are some data tabulations where the reference conditions are different, so values may differ.
- The temperature (T) and pressure (P) can be changed to obtain species properties at different conditions.
- Users can choose to display the data in either mass or mole basis. This is done via the Mass Basis check box, it toggles between the two options.
and 
: The SpeciesTag buttons toggles between the short and long species names.
: Pressing the CopytoClipboard button will add selected Properties Data onto the clipboard.
: The Reports button allows the user to copy selected data onto the clipboard.
and 
: These buttons allow the user to filter the species to display only species that meet certain criteria. See Species Filter for details on how the species filter is used.
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