Source: https://guthlabs.ai/docs/instruments/hess-s-law-enthalpy-calculator/implementation/

instrument implementation / implementation-contract

# Hess's Law Enthalpy Calculator implementation

A source-bound implementation contract for Hess's Law Enthalpy Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## 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-clean

**Evidence ID**: t8-013

**Effect**: Computation or source lookup only

## Input and validation requirements

- Division by zero or singular-system hazards can occur if the reaction matrix is rank-deficient; the solver must report underdetermined or inconsistent inputs.

- A supplied reaction may be unbalanced in atoms or charge; this must be rejected before solving.

- Missing or inconsistent phase labels can silently produce an incorrect enthalpy.

- Mixing J, kJ, cal, kcal, or values reported per mole of different reference species can produce errors unless units and reaction extent are explicit.

- A zero or near-zero pivot requires numerical tolerance handling; exact rational stoichiometry is preferable where possible.

- The instrument should not claim a unique answer when multiple valid step combinations exist.

- Negative multipliers must be displayed clearly as reaction reversals, and fractional multipliers must be displayed without rounding that changes the target equation.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

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

````
{
  "inputs": {
    "target_equation": "CH4(g) + 2 O2(g) -> CO2(g) + 2 H2O(l)",
    "known_reactions": [
      {
        "id": "R1",
        "equation": "C(graphite) + O2(g) -> CO2(g)",
        "delta_H": "-393.51 kJ"
      },
      {
        "id": "R2",
        "equation": "H2(g) + 1/2 O2(g) -> H2O(l)",
        "delta_H": "-285.83 kJ"
      },
      {
        "id": "R3",
        "equation": "CH4(g) -> C(graphite) + 2 H2(g)",
        "delta_H": "+74.85 kJ"
      }
    ]
  },
  "expected_outputs": {
    "overall_delta_H": "-890.32 kJ",
    "step_multipliers": {
      "R1": "1",
      "R2": "2",
      "R3": "1"
    },
    "oriented_steps": [
      "R1 as written",
      "2 × R2 as written",
      "R3 as written"
    ]
  },
  "reference_data": {
    "combined_equation": "R1 + 2R2 + R3 = CH4(g) + 2 O2(g) -> CO2(g) + 2 H2O(l)",
    "method": "Signed stoichiometric linear combination"
  },
  "working": "R1 + 2R2 + R3: C + O2 -> CO2; 2H2 + O2 -> 2H2O; CH4 -> C + 2H2. Cancel C and 2H2 from opposite sides. Remaining equation: CH4 + 2O2 -> CO2 + 2H2O. Arithmetic: ΔH = 1(-393.51) + 2(-285.83) + 1(+74.85) = -393.51 - 571.66 + 74.85 = -965.17 + 74.85 = -890.32 kJ."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/hess-s-law-enthalpy-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/hess-s-law-enthalpy-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/hess-s-law-enthalpy-calculator/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche8/tranche8-results.json`