Decomposition Analysis¶

PHOENIX calculates the maximum heat of decomposition (ΔHd) to predict energy release potential.

Overview¶

The maximum heat of decomposition represents the theoretical maximum energy release when a compound decomposes to its most thermodynamically stable products.

\[ \Delta H_d = \Delta H_f(\text{products}) - \Delta H_f(\text{reactant}) \]

Negative values indicate exothermic decomposition (energy release).

Basic Usage¶

from phoenix import Compound

compound = Compound.from_smiles("c1ccccc1[N+](=O)[O-]")  # Nitrobenzene
decomp = compound.max_decomposition()

print(f"ΔHd = {decomp.delta_hd_kJ_mol:.1f} kJ/mol")
print(f"ΔHd = {decomp.delta_hd_cal_g:.1f} cal/g")

DecompositionResult¶

The max_decomposition() method returns a DecompositionResult:

Attributes¶

Attribute	Type	Description
`delta_hd_kJ_mol`	float	ΔHd in kJ/mol (negative = exothermic)
`delta_hd_cal_g`	float	ΔHd in cal/g
`products`	dict[str, float]	Decomposition products and moles
`reactant_hf_kJ_mol`	float	Reactant ΔHf°
`products_hf_kJ_mol`	float	Total products ΔHf°
`gas_volume_L_g`	float	Gas volume at temperature
`gas_moles`	float	Total moles of gas
`gas_composition`	dict[str, float]	Gas mole fractions
`gas_temperature_K`	float	Temperature for gas calculation
`method`	str	'hierarchy' or 'lp'

Example¶

decomp = compound.max_decomposition()

# Energy release
print(f"ΔHd = {decomp.delta_hd_cal_g:.1f} cal/g")

# Products
print("\nDecomposition products:")
for product, moles in decomp.products.items():
    if moles > 0.01:
        print(f"  {product}: {moles:.3f} mol")

# Gas generation
print(f"\nGas generation: {decomp.gas_volume_L_g:.4f} L/g")
print(f"Gas moles: {decomp.gas_moles:.2f} mol/mol")

Calculation Methods¶

Hierarchy Method (Default)¶

Uses CHETAH analytical priority rules:

decomp = compound.max_decomposition(method="hierarchy")

The hierarchy follows thermodynamic priorities:

Priority	Reaction	Product
1	F + H → HF	Hydrogen fluoride
2	N → ½N₂	Nitrogen gas
3	P + O → ¼P₄O₁₀	Phosphorus pentoxide
4	H + O → ½H₂O	Water
5	C + O → ½CO₂	Carbon dioxide
6	S + O → SO₂	Sulfur dioxide
7	C + ½O → CO	Carbon monoxide
8	Cl + H → HCl	Hydrogen chloride
9	Br + H → HBr	Hydrogen bromide
10	C → C(s)	Graphite
11	H → ½H₂	Hydrogen gas
12	S → S(s)	Solid sulfur
13	Halogens → X₂	Diatomic halogens

LP Method¶

Uses Linear Programming optimization to find the mathematically optimal solution:

decomp = compound.max_decomposition(method="lp")

LP minimizes total product enthalpy subject to atom balance constraints.

Comparing Methods¶

Use method="both" to compare:

comparison = compound.max_decomposition(method="both")

print(f"Hierarchy: {comparison.hierarchy_result.delta_hd_cal_g:.1f} cal/g")
print(f"LP: {comparison.lp_result.delta_hd_cal_g:.1f} cal/g")
print(f"Deviation: {comparison.deviation_percent:.2f}%")

The DecompositionComparison object provides:

Attribute	Type	Description
`hierarchy_result`	DecompositionResult	Hierarchy method result
`lp_result`	DecompositionResult	LP method result
`deviation_percent`	float	% deviation between methods
`hierarchy_delta_hd`	float	Shortcut to hierarchy ΔHd
`lp_delta_hd`	float	Shortcut to LP ΔHd

When Methods Differ¶

Methods typically agree for: - Simple molecules - Complete oxidation scenarios

Methods may differ for: - Complex molecules with many possible products - Partially oxidized systems

# Example: Check for significant deviation
comparison = compound.max_decomposition(method="both")

if comparison.deviation_percent > 5:
    print("Warning: Methods disagree significantly")
    print(f"  Hierarchy: {comparison.hierarchy_delta_hd:.1f} kJ/mol")
    print(f"  LP: {comparison.lp_delta_hd:.1f} kJ/mol")

Gas Generation¶

Basic Gas Data¶

decomp = compound.max_decomposition()

print(f"Total gas: {decomp.gas_moles:.2f} mol/mol")
print(f"Volume: {decomp.gas_volume_L_g:.4f} L/g")

Gas Composition¶

decomp = compound.max_decomposition()

print("Gas composition (mole fractions):")
for gas, fraction in decomp.gas_composition.items():
    print(f"  {gas}: {fraction*100:.1f}%")

Temperature Effects¶

Gas volume depends on temperature:

# Default (298.15 K)
decomp_298 = compound.max_decomposition()

# Elevated temperature
decomp_500 = compound.max_decomposition(gas_temperature_K=500)

print(f"Gas at 298 K: {decomp_298.gas_volume_L_g:.4f} L/g")
print(f"Gas at 500 K: {decomp_500.gas_volume_L_g:.4f} L/g")

The ideal gas law is used:

\[ V = \frac{n \cdot R \cdot T}{P \cdot MW} \]

Product Distribution¶

Accessing Products¶

decomp = compound.max_decomposition()

# All products
print("All products:")
for product, moles in decomp.products.items():
    print(f"  {product}: {moles:.4f} mol")

# Filter significant products
print("\nSignificant products (>0.01 mol):")
for product, moles in decomp.products.items():
    if moles > 0.01:
        print(f"  {product}: {moles:.3f} mol")

Product Enthalpies¶

Reference formation enthalpies used:

Product	ΔHf° (kJ/mol)	Phase
HF	-273.30	gas
N₂	0.0	gas
P₄O₁₀	-2984.0	solid
H₂O	-241.83	gas
CO₂	-393.52	gas
SO₂	-296.81	gas
CO	-110.53	gas
HCl	-92.31	gas
HBr	-36.29	gas
C (graphite)	0.0	solid
H₂	0.0	gas

Practical Examples¶

Comparing Different Compounds¶

from phoenix import Compound

smiles_data = [
    ("CCO", "Ethanol"),
    ("c1ccccc1[N+](=O)[O-]", "Nitrobenzene"),
    ("Cc1c([N+](=O)[O-])cc([N+](=O)[O-])cc1[N+](=O)[O-]", "TNT"),
]

for smiles, name in smiles_data:
    compound = Compound.from_smiles(smiles)
    decomp = compound.max_decomposition()

    print(f"\n{name}:")
    print(f"  ΔHd = {decomp.delta_hd_cal_g:.0f} cal/g")
    print(f"  Gas = {decomp.gas_volume_L_g:.4f} L/g")

Energy Balance Analysis¶

compound = Compound.from_smiles("c1ccccc1[N+](=O)[O-]")
decomp = compound.max_decomposition()

# Energy balance
print("Energy Balance:")
print(f"  Reactant ΔHf°: {decomp.reactant_hf_kJ_mol:.1f} kJ/mol")
print(f"  Products ΔHf°: {decomp.products_hf_kJ_mol:.1f} kJ/mol")
print(f"  ΔHd: {decomp.delta_hd_kJ_mol:.1f} kJ/mol")

# Verify calculation
calculated = decomp.products_hf_kJ_mol - decomp.reactant_hf_kJ_mol
print(f"\nVerification:")
print(f"  Calculated: {calculated:.1f} kJ/mol")
print(f"  Reported: {decomp.delta_hd_kJ_mol:.1f} kJ/mol")

Oxygen-Limited Decomposition¶

# Oxygen-deficient compound
compound = Compound.from_smiles("CCCCCC")  # Hexane

decomp = compound.max_decomposition()

print(f"Hexane decomposition:")
print(f"  OB% = {compound.oxygen_balance:.1f}%")
print(f"  ΔHd = {decomp.delta_hd_cal_g:.1f} cal/g")

print("\nProducts (no oxygen available):")
for product, moles in decomp.products.items():
    if moles > 0.01:
        print(f"  {product}: {moles:.2f} mol")

Error Handling¶

Decomposition Errors¶

from phoenix import Compound, DecompositionError

try:
    compound = Compound.from_smiles("CCO")
    decomp = compound.max_decomposition()
except DecompositionError as e:
    print(f"Decomposition failed: {e.reason}")
    if e.formula:
        print(f"  Formula: {e.formula}")

LP Solver Failures¶

If LP fails, it falls back to hierarchy:

import warnings

# LP failure triggers warning and fallback
decomp = compound.max_decomposition(method="lp")
# Warning: LP solver failed: ... Falling back to hierarchy method.

Next Steps¶

Hazard Evaluation: Complete hazard assessment
Reactions: Reaction thermodynamics
API Reference: DecompositionResult API