CHETAH predicts potential hazards of compounds from thermochemical properties, most of which are estimated using Benson's method of group additivity for gases. Even though CHETAH makes predictions for gas phase properties, energy release evaluations are valid for gas, liquid, or solid materials. Group additivity methods assume that each portion of a molecule contributes an increment to the heat capacity, heat of formation, and entropy of the molecule. When heat capacity data for groups are missing, CHETAH uses less accurate estimations methods.
CHETAH can be used to perform the following functions by simple menu selections:
Areas that are beyond the scope of this program include:
- Classify a material or mixture with respect to its ability to decompose with violence when subjected to severe impact.
- Calculate the ENTHALPY OF COMBUSTION for a compound or mixture
- Calculate THERMOCHEMICAL PROPERTIES for REACTIONS: ∆Cprxn, ∆Hrxn, ∆Srxn, ∆Grxn, logK
- Calculate THERMOCHEMICAL PROPERTIES for COMPOUNDS: Cp, S, ∆Hf, ∆Gf, logKf, Free Energy Function (G-H)/T, HT-H298
- Estimate LOWER FLAMMABLE LIMITS, and other flammability properties
- BUILD COMPOUNDS from library or user-entered groups for gases, liquids, or solid crystals
- BUILD CRYSTALS from ionic groups
- Enter PRIVATE THERMOCHEMICAL DATA (Benson groups, gases, solids, or liquids)
- View THERMOCHEMICAL DATA in CHETAH’s database
- Modify previous CHETAH sessions
- Generate reports.
- CORRECTION OF IDEAL GAS VALUES TO LIQUID OR SOLID PHASES This version of CHETAH can predict thermodynamic properties of solids and liquids using a predictive method based on Benson’s method. However the most general predictive method is based on ideal gas values. Many compounds can only have their properties predicted as ideal gases in CHETAH. This program cannot correct the ideal gas values back to condensed values. This can be an important consideration when calculating heats of reactions. Accurate heats require true representation of the states of reactants and products. In some cases, the gas phase heat of reaction may not differ significantly from the condensed phase value due to a cancellation of corrections. NOTE: The hazard evaluation portion of CHETAH (ERE option) classifies materials in the condensed state based on gas phase thermodynamic properties. This is feasible because the correlations used by CHETAH were developed using data that were measured for condensed phase materials and because phase transition energies are small with respect to the amount of energy that is required to generate a violent explosion. CHETAH uses gas state thermodynamics to classify materials that are in any of the gas, liquid, or solid states
- KINETICS. CHETAH cannot predict rates of chemical reactions in the classic sense of determination of Arrhenius parameters.