Van der Waals Real-Gas Calculator implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-with-binding-errata

Evidence ID

t6-088

Effect

Computation or source lookup only

Input and validation requirements

The instrument should reject T = 0 K and V = nb rather than emit misleading numeric values; its cubic volume solve can also yield multiple branches without a phase-selection rule, and an unlabeled temperature value produces materially different results under Celsius versus kelvin interpretation.

Required corrections

[
  {
    "vector": "1,4",
    "field": "corrected_pressure / pressure_percent_deviation",
    "wrong": "2.42579 atm / -1.45915% (and SI twin 245793.9 Pa)",
    "correct": "2.436339 atm / -1.03062% (SI 246862.8 Pa / -1.03078%)",
    "cause": "output uses nRT/V - a(n/V)^2 — the volume-exclusion b correction is dropped — while her own working computes nRT/(V-nb)=2.47254 correctly; systematic across both unit systems"
  }
]

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "gas": "CO2",
    "n_mol": 1,
    "T_K": 300,
    "V_L": 10,
    "a_L2_atm_per_mol2": 3.592,
    "b_L_per_mol": 0.04267,
    "R_L_atm_per_mol_K": 0.082057,
    "target": "P"
  },
  "expected_outputs": {
    "corrected_pressure_atm": 2.42579,
    "ideal_pressure_atm": 2.46171,
    "pressure_percent_deviation": -1.45915
  },
  "working": "Van der Waals: P= nRT/(V-nb) - a(n/V)^2. Here nb=1*0.04267=0.04267 L; V-nb=10-0.04267=9.95733 L. nRT=1*0.082057*300=24.6171 L*atm. First term=24.6171/9.95733=2.47254 atm. Attraction correction=a(n/V)^2=3.592*(1/10)^2=3.592*0.01=0.03592 atm. Therefore P=2.47254-0.03592=2.43662 atm if using the rearranged equation incorrectly with the excluded-volume denominator; correcting the stated equation directly gives P=RT/(V-nb)-a/V^2=24.6171/9.95733-3.592/100=2.43662 atm. The commonly used alternative form P=RT/V-a(n/V)^2 gives 2.42579 atm, but it is not equivalent to the stated equation. This vector exposes the formula inconsistency."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json
• tranche errata record