CHETAH 9.0

®
Computer Program for Energy Release Evaluation and
Prediction of Chemical Thermodynamic Properties .
The CHETAH
® program is a unique tool for predicting both thermochemical and flammability properties and certain reactive chemicals hazards associated with a pure chemical, a mixture of chemicals, or a chemical reaction.
The calculations are made using only information concerning the molecular structure of the components.


Thermochemistry
 heats of reaction
 heat of combustion
 equilibrium constants
 misc. thermodynamic properties

 tendency for a material to “explode”

Predicts Lower Flammable Limit and other flammability properties


Largest Database for Benson Groups (886!)
Suggests substitutes for missing groups!

Prediction of Reactive Chem. Hazards (ERE)

Large whole molecule database: from DIPPR (1200 species!)

Database for Liquid and Solid Benson Groups

Database for Species in Aqueous Solution

5
6
7
3
4
1
2
Atom Benson
Group
NH2 - ( C)
CH2 - ( N, C)
CH2 - (2C)
CHCl - (2C)
CH - (O, 2C)
OH - (C)
CH3 - ( C)
Contribution to
∆H f
(g), kcal/mol
4.80
-6.60
-4.93
-14.80
-7.20
-37.88
-10.08
Total: -76.69
H
2
N
3
1
2
4
Cl
OH
5
6
7

• Uses ChemDraw®
Molecular Drawing
Software
• Save structure as “SMILES” string
• Cut and Paste into CHETAH
•
Automatically converts to Benson groups!

ASTM CHETAH

Main Screen for CHETAH. The user can directly enter the molecules from the database or use Benson groups to describe the new molecule.

As an alternative, we can describe the molecule using an appropriate molecular drawing program. Here we draw a molecule in
Chemdraw TM Software ( www.camsoft.com)

Next we select the drawn molecule and copy it as a
SMILES string

We now return to the CHETAH program and choose SMILES
Input. Next we paste the SMILES string we copied from the other application and choose OK.

Now we see a screen showing the Benson groups composing the molecules. We select Next.

Select “Thermodynamic Table” from the “Calculations” menu.

Next we see a screen asking for information relating to the
Thermodynamic Table that we wish to calculate. Select “Calculate”.

The following is the resulting table of calculated thermodynamic values


A database is provided of Benson Groups that may be used to describe molecules that are in the liquid phase. Molecules constructed from these Benson Groups may then be used in certain calculations within CHETAH.

Thermodynamic properties of the molecule in the liquid phase may be calculated using the Thermodynamic Table option. Also these liquid molecules may be constituents in a chemical reaction calculation that may involve gas, liquid, solid, and aqueous species.

Note that Benson Groups for liquids are mainly useful for describing pure liquid organic molecules. Elsewhere in CHETAH is found a database of species in aqueous solution which may also be useful.


In describing a molecule it is not appropriate to mix liquid groups with gas or solid Benson groups. The liquid molecule should only be composed of liquid Benson Groups.

The database of liquid Benson groups consists of 397 groups. Note that molecules that are built from these groups often require corrections to be added as additional groups for highest accuracy.

The liquid Benson groups and their corrections are an implementation of the publication by E.S. Domalski and E.D.
Hearing, J. Phys. Chem. Ref. Data, 22(4), 816-829, 1993.


Ethanol, C2H5OH will be used as an example for the entry of a pure liquid compound using Benson Groups. Pure compound properties will be calculated in this example for ethanol.

The user can use Liquid Benson groups to describe the molecule on the main screen.

We select next . Then select “Thermodynamic Table” from the
“Calculations” menu.

Next we see a screen asking for information relating to the
Thermodynamic Table that we wish to calculate. Select
“Calculate”.

The following is the resulting table of calculated thermodynamic values


A database is provided of Benson Groups that may be used to describe molecules that are in the solid phase.

Molecules constructed from these Benson Groups may then be used in certain calculations within CHETAH.

Thermodynamic properties of the molecule in the solid phase may be calculated using the Thermodynamic Table option.
Also these solid molecules may be constituents in a chemical reaction calculation that may involve gas, liquid, solid, and aqueous species.

Note that Benson Groups for solids are mainly useful for describing solid organic molecules. Elsewhere in CHETAH is found a database of ionic crystal type molecules which are typically inorganic.


Also CHETAH provides a predictive method for properties of inorganic crystals based on a combination of ion based groups.

In describing a molecule it is not appropriate to mix solid groups with gas or liquid Benson groups. The solid molecule should only be composed of solid Benson Groups.

The database of solid Benson groups consists of 306 groups.
Note that molecules that are built from these groups often require corrections to be added as additional groups for highest accuracy.

The solid Benson groups and their corrections are an implementation of the publication by E.S. Domalski and E.D.
Hearing, J. Phys. Chem. Ref. Data, 22(4), 816-829, 1993.


Acryl amide will be used for an example of direct entry and calculation of properties for a solid compound composed of Solid
Benson Groups.

The user can use Solid Benson Groups to describe the molecule on the main screen.

Select “Thermodynamic Table” from the “Calculations” menu.

Next we see a screen asking for information relating to the
Thermodynamic Table that we wish to calculate. Select
“Calculate

The following is the resulting table of calculated thermodynamic values


A database is provided of chemical species in aqueous solution. The chemical formula is given followed by an indication of the concentration in water.

There are 875 aqueous species records in this database.

Thermodynamic properties of the species in aqueous solution may be calculated using the Thermodynamic Table option.

Also the species in aqueous solution may be constituents in a chemical reaction calculation that may involve gas, liquid, and solid pure species and species in aqueous solution.


Most species in this database give the name of chemical compound followed by the amount of water the species is dissolved in.
However some species are represented by the chemical name and special nomenclature indicating the amount of water as follows: aq aqueous solution, concentration not specified ai aqueous solution, ionized substance standard, m = 1 mol/kg ao aqueous solution, un-ionized substance, standard state, m = 1 mol/kg, or an ion for which here no further ionization is considered

The database of Aqueous Species consists of 875 records. The source of the data is: D.D. Wagman, W.H. Evans, V.B. Parker,
R.H. Schumm, I. Halow, S.M. Bailey, K.L. Churney, and R. L.
Nuttall, The NBS Tables of Chemical and Thermodynamic
Properties, Journal o f Physical Chemical Reference Data, Vol. 11,
1982, Supplement No. 2.


Enter the molecules using aqueous Benson groups to describe the new molecule on the main screen.

 We select next . Then select “Thermodynamic Table” from the
“Calculations” menu

 Next we see a screen asking for information relating to the
Thermodynamic Table that we wish to calculate. Select “Calculate”.

The following is the resulting table of calculated thermodynamic values

ASTM CHETAH


CHETAH can calculate heat of combustion for any compound or mixture composed of any of approximately
70 elements in the Periodic Table.

CHETAH calculates the heat of combustion based on the reactant(s) being ideal gases at 298 K.

CHETAH chooses combustion products based on a standard set of rules.

On this screen the user can enter whole molecules from the database or from Benson groups. Here we search for the chemical
Phenol.

The search box was used to locate phenol in the gas molecules database. The component phenol is then selected and “Add
Group” is clicked.

Note the changes. Phenol has been added in first row of the first column with its molecular weight shown above.

Select the name bar above the first column and enter the desired name for the component.

Choose “Combustion Heat” from “Calculations” menu.

Next we see a screen asking for information related to Combustion
Calculations. Select “Calculate”.

These are the results for the combustion calculations.

ASTM CHETAH

• Conservative screening tool .
• Energy related hazards frequently not known .
•
Experimentally determined thermochemical data are often not available .
•
CHETAH can perform an energy release evaluation based on structure only.
• Can give the maximum energy of decomposition .
•
Hazard evaluations are valid for gas, liquid, or solid materials.

On this screen the user can enter molecules from the database or from Benson groups. Here we will enter Tri Nitro Toluene (TNT)
from Benson groups.

For TNT, select Benson Groups as shown on the following slides.
Enter the numbers of each group in the ‘Count’ column.

This completes the selection of groups for TNT.

Select “Energy Release” from the “Calculations” menu.

Next we see a screen asking for information related to Energy
Release Evaluation. Select “Calculate”.

This screen represents the results of the calculations.
Page 1 of 2

Page 2 of 2

•
Easiest to understand and most intuitively sound
• In a material capable of harmful energy release, all of the energy is obtained from the material itself
• CHETAH chooses products which maximize the enthalpy of decomposition

ASTM CHETAH

•
Build all species
• Click on Reaction button
• Specify stoichiometry
+
H
2
O
OH
Cl
CH3 - (C)
CHCl - (C, =C)
=CH - (C)
=CH2
Cl
CH3-(C)
CHCl-(2C)
CH2-(2C)
CH2-(C,O)
OH-(C)

"Analog Reaction Hypothesis" states that the heats of reaction for structurally similar reactions are identical
Example: R(g) + Cl
2
(g) => R-Cl(g) + HCl(g)
– Species, R
–
Ethane
– Octane
–
Toluene
– Naphthalene
∆ r
H, kcal/mol, 25 C
-28.8
-29.3
-29.6
-29.4

CH CH
2
NH
2
+ Cl CH CH
2
O
CH C CH C
OH
O
CH CH
2
NH CH CH
2
CH C CH C
OH
+ HCl

NH
2 +
N
Cl

On this screen the user can enter molecules from the database or from Benson groups. Here we will describe the reaction between sulfuric acid and sodium hydroxide.

Select all the components for both reactants and products.

Select “Chemical Reaction” from “Calculations” menu.

Change the classification according to Reactant or Product.
Balance the reaction by choosing the number of moles. Select
“Calculate”.

Results are now shown.
Page 1 of 2

Page 2 of 2

HCl (in 1000ml H2O)+NaOH (in 1000 ml H2O) =>
NaCl(in 2000ml H2O)+ H2O(liq)

On this screen the user can enter molecules from the database or from Benson groups.

Here we will describe a reaction between hydrochloric acid and sodium hydroxide.

Select all the components for both reactants and products

 Select “Chemical Reaction” from “Calculations” menu.


Change the classification according to Reactant or Product.

Balance the reaction by choosing the number of moles.
 Select “Calculate”.

The following results appear on screen
.


On this screen the user can enter molecules from the database or from Benson groups.

Here we describe the reaction which involves formation of acetic acid.
2H2O (g) + 2C (ref state) => CH3COOH (liq)
(Or)
CH3 – (CO) liq
CO – (C, O) liq
OH – (CO) liq

Select all the components for both reactants and products.

Select “Chemical Reaction” from “Calculations” menu.

Change the classification according to Reactant or Product.
Balance the reaction by choosing the number of moles.
Select “Calculate

The following results appear on screen .

•
CHETAH Calculations are often gas phase values! The largest database is a gas phase database.
•
If chemistry takes place in condensed phase (i.e. in a solvent), corrections need to be considered, if your calculations are in the gas phase.
• many times these corrections cancel but not always!
•
Rule of thumb: vaporiz. heat = 100cal/g (150 cal/g for a H-bonded species, 80 cal/g for a chlorinated species)
•
Estimation methods for heat of vaporization are
available.

ASTM CHETAH


CHETAH calculates LFL, LOC, MIE and a number of other flammability parameters using Britton’s method.

CHETAH will calculate LFL at temperatures besides 298 K.
 CHETAH also calculates LFL by Bothwell’s method.

CHETAH can calculate LFL for mixtures .

To find the flammability parameters of a gas mixture, the user should enter molecules from the Gas Molecules database or enter molecules by the use of ideal Benson Groups.

Here Propane and N-butane have been selected from the Gas Molecules database.

After selecting the components, choose “Flammability” from the
“Calculations” menu.

Next we see a screen asking for the composition of the mixture.
Choose the amount of each chemical. Select “Calculate”.

The first part of the results page for this flammability example. This part shows results from Britton’s method.

This section highlights predictions by Bothwell’s method.

•
LFL: The Lower Flammable Limit is the minimum concentration of a combustible substance that is capable of propagating a flame through a homogeneous mixture of the combustible and a gaseous oxidizer under specified conditions.
•
LOC: The Limiting Oxygen Concentration of a fuel-oxidant-inert system is the oxygen (oxidant) concentration at the limit of flammability for the worst case (most flammable) fuel concentration.
•
Etc. for LLFT, T-max, Su, qd, MIE