Gas mole fraction from partial pressure
Find what share of a gas mixture one component makes up: oxygen at 0.21 atm in air at 1 atm has a mole fraction of 0.21, or 21 %. Both pressures just need the same unit. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Partial pressure
- 0.21
- Total pressure
- 1
- Mole fraction
- 0.21
- Mole percent
- 21
Dalton’s law of partial pressures implies a simple inverse for gas composition: the mole fraction of a component equals its partial pressure divided by the total absolute pressure of the mixture, yi equals Pi over P. Students checking multi-gas homework, chemistry teachers building answer keys, process engineers converting analyzer partial pressures into dry-basis mole fractions, and lab technicians relating sensor readings to mixture composition all need the same contract—positive total pressure, a non-negative component partial pressure in matching units, and a structured mole-fraction result without re-deriving the divide by hand.
What mole fraction from partial pressure means and which inputs you must send
In introductory chemistry and thermodynamics, Dalton’s law partitions total pressure among ideal-gas components so each partial pressure is the mole fraction times total pressure; rearranging gives the composition formula students and engineers actually search for when the sensor reports pressures: mole fraction yi equals partial pressure Pi divided by total pressure P. Search intent clusters around gas mole fraction from partial pressure calculator, Dalton law composition, yi equals Pi over P, component mole fraction gas mixture, and oxygen mole fraction from partial pressure.
People want a numeric answer they can check against a worksheet, embed in a lab report, or feed into a larger pipeline—not only a reminder that the formula exists. Keep units consistent: the engine divides only; it does not convert atmospheres to pascals or gauge readings to absolute pressure. Zero total pressure is always rejected because division by zero is undefined for this product, and negative total pressure is rejected so the contract stays honest for laboratory work.
How this calculator validates pressures and applies yi = Pi / P
Numeric strings that parse to finite numbers are accepted so web forms and CSV-style pipelines can pass values without an extra cast. Partial pressure must be non-negative; total pressure must be strictly positive and must not be zero—the product contract names zero total pressure as the hard invalid case. There is no Raoult vapor-liquid branch, no real-gas fugacity correction, and no unit conversion service—this is pure Dalton for ideal mixtures.
If partial pressure exceeds total pressure the ratio may exceed one; that is returned so data-entry mistakes surface, and callers that require yi in the closed unit interval can validate that range in their own UI after reading the response.
What you can do with it
Homework and multi-gas drills
Students and graders convert oxygen or nitrogen partial pressures and total pressure into mole fraction and mole percent, with clear rejection when total pressure is zero by mistake.
Process and lab composition sketches
Quick structured estimates of component mole fraction from analyzer partial pressures without standing up a full process simulator or spreadsheet.
FAQ
What happens if total pressure is zero?
Zero total pressure makes yi = Pi / P undefined; non-positive total pressure is also rejected and not charged.
Can partial pressure exceed total pressure?
Yes. The engine still returns the ratio so data-entry mistakes surface.
Is the gas mole fraction calculator free?
The browser tool runs free on your device.
Does the calculator convert pressure units?
No. Keep partial pressure and total pressure in the same absolute unit family (atm, Pa, bar, or torr). The engine divides only and does not convert units.
Does it give the answer as a percentage too?
Yes. Next to the mole fraction you get the mole percent, which is the fraction multiplied by one hundred. A fraction of 0.21 therefore appears as 21 %, ready for a lab report or a composition table.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/chem/dalton-mole-fraction \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"partial_pressure":0.21,"total_pressure":1}'const res = await fetch("https://api.kit.forhosting.com/chem/dalton-mole-fraction", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"partial_pressure": 0.21,
"total_pressure": 1
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/dalton-mole-fraction",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"partial_pressure": 0.21,
"total_pressure": 1
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/dalton-mole-fraction", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"partial_pressure":0.21,"total_pressure":1}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"partial_pressure":0.21,"total_pressure":1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/dalton-mole-fraction", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"partial_pressure": 0.21,
"total_pressure": 1
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.dalton_mole_fraction",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
This capability computes that ratio deterministically, rejects a zero total pressure with a clear invalid_input error so notebooks and tutoring apps never see Infinity, and returns JSON that homework checkers and lightweight process helpers can pin in tests.
What mole fraction from partial pressure means and which inputs you must send
Send a positive total_pressure in any coherent absolute unit you already use for the problem (atmospheres, pascals, bar, or torr) and the component partial_pressure in that same unit. Aliases Pi, p_i, partial, P, P_total, and pressure are accepted so forms and scripts can match textbook variable names.
How this calculator validates pressures and applies yi = Pi / P
Send a JSON body with required partial_pressure and total_pressure. Every numeric field must be finite: missing required values, empty strings, non-numeric text, NaN, and Infinity all fail immediately with invalid_input before any result is returned, and failed validation is not charged. After validation the engine divides partial pressure by total pressure, multiplies by one hundred for mole percent, rounds to a stable decimal precision so the same input always yields the same JSON across JavaScript engines, and echoes both pressures. The response includes mole_fraction as the unitless ratio yi, mole_percent as one hundred times yi, formula always set to yi equals Pi over P, and method always dalton_mole_fraction so downstream code can branch without sniffing shapes.
API usage, pricing, classroom workflows, and practical limits
Call the free in-browser gas mole fraction calculator for homework checks, lecture demos, and quick air-composition mental math without installing a thermodynamics package. Choose absolute pressure units consistently on both sides of the ratio so the solved mole fraction stays dimensionless and independent of the unit family your sensors or textbook expect. Use the prepaid API when a tutoring platform, coding-assessment sandbox, curriculum generator, process sketch tool, or gas-analysis pipeline needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with the forward Dalton partial-pressure tool when the next step is converting mole fractions back to component pressures, or with ideal-gas tools when concentration from partial pressure is required. Authors shipping SDKs can map mole_fraction into composition tables and mole_percent into student-facing labels—the same two numbers learners write when they apply the inverse Dalton formula by hand on multi-gas problems.
Integration use cases
Deterministic fixtures for chemistry tests
Pipelines that seed unit tests or interactive science demos can call a pure yi=Pi/P oracle instead of reimplementing Dalton composition arithmetic in every language.
Technical questions
How do I calculate gas mole fraction from partial pressure?
Send JSON with partial_pressure (Pi) and total_pressure (P). The response returns mole_fraction as yi = Pi / P and mole_percent as 100·yi.