{"openapi":"3.1.0","info":{"title":"Vapor Pressure API","version":"1.0.0","description":"Vapor-pressure thermodynamics as an API, computed locally and deterministically. The clausius-clapeyron endpoint predicts the vapor pressure of a substance at a new temperature from a known reference point and the molar enthalpy of vaporization, using ln(P2/P1) = -ΔHvap/R·(1/T2 - 1/T1) with temperatures in kelvin — so from water boiling at 101.325 kPa at 373.15 K and ΔHvap ≈ 40.66 kJ/mol it returns about 42.6 kPa at 350 K. The enthalpy endpoint inverts the same relation: given two pressure/temperature points it solves for the molar enthalpy of vaporization, ΔHvap = -R·ln(P2/P1)/(1/T2 - 1/T1), in J/mol and kJ/mol. The antoine endpoint evaluates the Antoine equation log10(P) = A - B/(C + T) both ways — supply a temperature to get the vapor pressure, or a pressure to get the boiling temperature — defaulting to the water constants (°C and mmHg, so water reads 760 mmHg at 100 °C) but accepting any A, B, C for other substances. The gas constant R = 8.314462618 J/(mol·K). Everything is computed locally and deterministically, so it is instant and private. Ideal for chemical-engineering, process-simulation, distillation, HVAC, meteorology and chemistry-education app developers, boiling-point and phase-equilibrium tools, and lab software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is vapor pressure and boiling point; for humidity and dew point use a psychrometric API and for ideal-gas state use a gas-law API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/vaporpressure-api","description":"oanor gateway"}],"tags":[{"name":"VaporPressure"},{"name":"Meta"}],"components":{"securitySchemes":{"oanorKey":{"type":"apiKey","in":"header","name":"x-oanor-key","description":"Get your key at https://www.oanor.com/developer/keys"}}},"security":[{"oanorKey":[]}],"paths":{"/v1/antoine":{"get":{"operationId":"get_v1_antoine","tags":["VaporPressure"],"summary":"Antoine equation","description":"","parameters":[{"name":"temperature","in":"query","required":false,"description":"Temperature (°C) → pressure","schema":{"type":"string"},"example":"100"},{"name":"pressure","in":"query","required":false,"description":"Pressure (mmHg) → boiling temp","schema":{"type":"string"}},{"name":"a","in":"query","required":false,"description":"Antoine A (default water)","schema":{"type":"string"}},{"name":"b","in":"query","required":false,"description":"Antoine B","schema":{"type":"string"}},{"name":"c","in":"query","required":false,"description":"Antoine C","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"mode":"pressure_from_temperature","note":"Antoine: log10(P) = A - B/(C + T). With the default water constants T is in °C and P in mmHg (water boils at 760 mmHg at 100 °C).","inputs":{"a":8.07131,"b":1730.63,"c":233.426,"temperature":100},"pressure":760.086369,"log10_pressure":2.88086294,"constants_source":"water (default)"},"meta":{"timestamp":"2026-06-05T19:50:32.225Z","request_id":"c73f7863-d7c6-4864-9e5e-d6fd61ae7788"},"status":"ok","message":"Antoine equation","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/clausius-clapeyron":{"get":{"operationId":"get_v1_clausius_clapeyron","tags":["VaporPressure"],"summary":"Predict vapor pressure","description":"","parameters":[{"name":"p1","in":"query","required":true,"description":"Reference pressure","schema":{"type":"string"},"example":"101325"},{"name":"t1","in":"query","required":true,"description":"Reference temperature (K)","schema":{"type":"string"},"example":"373.15"},{"name":"t2","in":"query","required":true,"description":"Target temperature (K)","schema":{"type":"string"},"example":"350"},{"name":"enthalpy","in":"query","required":true,"description":"Molar enthalpy of vaporization (J/mol)","schema":{"type":"string"},"example":"40660"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"p2":42585.151901,"note":"Clausius–Clapeyron: ln(P2/P1) = -ΔHvap/R·(1/T2 - 1/T1). Temperatures in kelvin; P2 comes out in the same pressure unit as P1; ΔHvap in J/mol; R = 8.314462618 J/(mol·K).","inputs":{"p1":101325,"t1":373.15,"t2":350,"enthalpy":40660},"ln_p2_over_p1":-0.86682753},"meta":{"timestamp":"2026-06-05T19:50:32.338Z","request_id":"9b09aedd-73fb-44ee-9689-99180e1c7d32"},"status":"ok","message":"Clausius-Clapeyron vapor pressure","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/enthalpy":{"get":{"operationId":"get_v1_enthalpy","tags":["VaporPressure"],"summary":"Enthalpy of vaporization","description":"","parameters":[{"name":"p1","in":"query","required":true,"description":"Pressure at point 1","schema":{"type":"string"},"example":"101325"},{"name":"t1","in":"query","required":true,"description":"Temperature 1 (K)","schema":{"type":"string"},"example":"373.15"},{"name":"p2","in":"query","required":true,"description":"Pressure at point 2","schema":{"type":"string"},"example":"42585"},{"name":"t2","in":"query","required":true,"description":"Temperature 2 (K)","schema":{"type":"string"},"example":"350"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Two-point Clausius–Clapeyron solved for ΔHvap = -R·ln(P2/P1)/(1/T2 - 1/T1). Temperatures in kelvin, pressures in any consistent unit.","inputs":{"p1":101325,"p2":42585,"t1":373.15,"t2":350},"enthalpy_j_per_mol":40660.1673,"enthalpy_kj_per_mol":40.660167},"meta":{"timestamp":"2026-06-05T19:50:32.454Z","request_id":"7f1f185f-e0df-4ecc-86b5-761d03cd1992"},"status":"ok","message":"Enthalpy of vaporization","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/meta":{"get":{"operationId":"get_v1_meta","tags":["Meta"],"summary":"Spec","description":"","parameters":[],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"notes":"Clausius–Clapeyron uses kelvin; Antoine defaults to water constants with °C and mmHg. R = 8.314462618 J/(mol·K).","service":"vaporpressure-api","constants":{"default_antoine_water":{"A":8.07131,"B":1730.63,"C":233.426},"gas_constant_j_per_mol_k":8.314462618},"endpoints":{"GET /v1/meta":"This document.","GET /v1/antoine":"Antoine equation: temperature→pressure, or pressure→boiling temperature.","GET /v1/enthalpy":"Molar enthalpy of vaporization from two (P,T) points.","GET /v1/clausius-clapeyron":"Predict vapor pressure P2 at T2 from a reference (P1,T1) and ΔHvap."},"description":"Vapor pressure thermodynamics: Clausius–Clapeyron prediction, enthalpy of vaporization from two points, and the Antoine equation both ways."},"meta":{"timestamp":"2026-06-05T19:50:32.552Z","request_id":"81f716ac-8ced-4f0f-a32d-538dde1ff449"},"status":"ok","message":"Meta","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}}},"x-oanor-pricing":[{"slug":"free","name":"Free","price_cents_month":0,"monthly_call_quota":3600,"rps_limit":2,"hard_limit":true},{"slug":"starter","name":"Starter","price_cents_month":600,"monthly_call_quota":38000,"rps_limit":6,"hard_limit":true},{"slug":"pro","name":"Pro","price_cents_month":1800,"monthly_call_quota":182000,"rps_limit":15,"hard_limit":true},{"slug":"mega","name":"Mega","price_cents_month":5800,"monthly_call_quota":1120000,"rps_limit":40,"hard_limit":true}],"x-oanor-marketplace-url":"https://www.oanor.com/api/vaporpressure-api"}