{
  "id": "partial-pressure",
  "version": "05ecf426ba66",
  "status": "published",
  "name": "Partial Pressure Calculator",
  "question": "What is the partial pressure of a gas?",
  "summary": "Finds the partial pressure of one gas in a mixture with Dalton’s law: from its mole fraction and the total pressure, from its moles and the total moles, or from its moles, the volume and the temperature.",
  "category": "chemistry",
  "subcategory": "gases",
  "url": "https://www.acalculator.org/chemistry/partial-pressure-calculator",
  "markdown": "https://www.acalculator.org/chemistry/partial-pressure-calculator.md",
  "kind": "function",
  "method": "P_A = X_A × P_total, where X_A = n_A ÷ n_total. For one gas in a container: P_A = n_A × R × T ÷ V, with R = 8.31446261815324 J/(mol·K).",
  "assumptions": [
    "The gases are ideal and do not react with each other, so each gas acts as if it filled the container alone (Dalton’s law).",
    "Pressures are absolute; temperatures are absolute (K = °C + 273.15)."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "from": {
        "title": "Work from",
        "description": "The mole fraction and total pressure, the moles of the gas and of the whole mixture, or the moles, volume and temperature.",
        "type": "string",
        "enum": [
          "moles",
          "fraction",
          "gas"
        ]
      },
      "x": {
        "title": "Mole fraction (X)",
        "description": "The gas’s share of all the moles in the mixture, from 0 to 1 (0.21 for oxygen in dry air).",
        "type": "number",
        "exclusiveMinimum": 0,
        "maximum": 1
      },
      "n": {
        "title": "Moles of this gas",
        "description": "The amount of the gas you want the partial pressure of, in moles.",
        "type": "number",
        "minimum": 1e-15,
        "maximum": 1000000000000000
      },
      "nt": {
        "title": "Moles of all gases",
        "description": "The total amount of gas in the mixture, this gas included, in moles.",
        "type": "number",
        "minimum": 1e-15,
        "maximum": 1000000000000000
      },
      "P": {
        "title": "Total pressure",
        "description": "The pressure of the whole mixture (absolute).",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "pressure",
        "minimum": 1e-9,
        "maximum": 1000000000000
      },
      "V": {
        "title": "Volume",
        "description": "The volume of the container.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "volume",
        "minimum": 1e-12,
        "maximum": 1000000000
      },
      "T": {
        "title": "Temperature",
        "description": "The temperature of the gas; above absolute zero.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "temperature",
        "minimum": 0.000001,
        "maximum": 1000000000
      }
    }
  },
  "outputs": {
    "result": {
      "label": "Partial pressure",
      "description": "The partial pressure, to 6 significant figures, in kPa and atm.",
      "format": "text"
    },
    "kpa": {
      "label": "Partial pressure (kPa)",
      "description": "The partial pressure in kilopascals.",
      "format": "number"
    },
    "atm": {
      "label": "Partial pressure (atm)",
      "description": "The partial pressure in standard atmospheres.",
      "format": "number"
    },
    "mmhg": {
      "label": "Partial pressure (mmHg)",
      "description": "The partial pressure in millimeters of mercury.",
      "format": "number"
    },
    "fraction": {
      "label": "Mole fraction",
      "description": "The gas’s share of the moles in the mixture (when known).",
      "format": "number"
    },
    "percent": {
      "label": "Share of the mixture (%)",
      "description": "The mole fraction as a percent (when known).",
      "format": "number"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "from": "moles",
      "x": 0.21,
      "n": 2.83,
      "nt": 11.24,
      "P": "192 kPa",
      "V": "10 L",
      "T": "35 °C"
    },
    "outputs": {
      "result": "48.3416 kPa (0.477095 atm)",
      "kpa": 48.34163701067616,
      "atm": 0.47709486316976224,
      "mmhg": 362.5920443518646,
      "fraction": 0.251779359430605,
      "percent": 25.177935943060497
    },
    "text": "The partial pressure is 48.3416 kPa (0.477095 atm)."
  },
  "examples": [
    {
      "given": {
        "from": "moles",
        "n": 2.83,
        "nt": 11.24,
        "P": 192000
      },
      "expect": {
        "kpa": 48.34163701067616,
        "x": 0.251779359430605
      },
      "source": "OpenStax, Chemistry 2e, §9.3 Stoichiometry of Gaseous Substances, Mixtures, and Reactions (Dalton’s law: P_A = X_A × P_Total), https://openstax.org/books/chemistry-2e/pages/9-3-stoichiometry-of-gaseous-substances-mixtures-and-reactions, Example 9.15 The Pressure of a Mixture of Gases: X(O₂) = 0.252, P(O₂) = 48.4 kPa; Python 3"
    },
    {
      "given": {
        "from": "gas",
        "n": 0.0025,
        "V": 0.01,
        "T": 308.15
      },
      "expect": {
        "atm": 0.006321494339461932
      },
      "source": "OpenStax, Chemistry 2e, §9.3 Stoichiometry of Gaseous Substances, Mixtures, and Reactions (Dalton’s law: P_A = X_A × P_Total), https://openstax.org/books/chemistry-2e/pages/9-3-stoichiometry-of-gaseous-substances-mixtures-and-reactions, Example 9.14 The Pressure of a Mixture of Gases: P(H₂) = 6.32 × 10⁻³ atm; Python 3"
    },
    {
      "given": {
        "from": "fraction",
        "x": 0.21,
        "P": 101325
      },
      "expect": {
        "atm": 0.21,
        "kpa": 21.27825,
        "result": "21.2783 kPa (0.21 atm)"
      },
      "source": "OpenStax, Chemistry 2e, §9.3 Stoichiometry of Gaseous Substances, Mixtures, and Reactions (Dalton’s law: P_A = X_A × P_Total), https://openstax.org/books/chemistry-2e/pages/9-3-stoichiometry-of-gaseous-substances-mixtures-and-reactions; hand calculation in content.mdx: 0.21 × 101.325 kPa = 21.27825 kPa"
    }
  ],
  "sources": [
    "OpenStax, Chemistry 2e, section 9.3 Stoichiometry of Gaseous Substances, Mixtures, and Reactions: Dalton’s law of partial pressures, P_A = X_A × P_Total, X_A = n_A ÷ n_Total; Examples 9.14 and 9.15. CC BY 4.0, retrieved 2026-10-03. https://openstax.org/books/chemistry-2e/pages/9-3-stoichiometry-of-gaseous-substances-mixtures-and-reactions",
    "NIST, CODATA value of the molar gas constant R = 8.314462618... J/(mol·K), exact. Retrieved 2026-10-03. https://physics.nist.gov/cgi-bin/cuu/Value?r"
  ],
  "related": [
    "ideal-gas-law",
    "combined-gas-law",
    "charles-law"
  ],
  "changelog": []
}