Raoult's law two-component calculator
A liquid with 0.4 of component 1 (pure vapor pressure 92) and 0.6 of component 2 (35) has partial pressures of 36.8 and 21, a total of 57.8 in the same unit. You also get the vapor composition. Free in your browser.
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Worked example
- Mole fraction 1
- 0.4
- Mole fraction 2
- 0.6
- Pure vapor pressure 1
- 92
- Pure vapor pressure 2
- 35
- Partial pressure 1
- 36.8
- Partial pressure 2
- 21
- Total vapor pressure
- 57.8
- Vapor mole fraction 1
- 0.6366782007
Raoult's law for two volatile liquids states that each component contributes a partial vapor pressure equal to its liquid mole fraction times its pure-component vapor pressure at the same temperature. For an ideal binary mixture the measurable total vapor pressure is therefore the sum P equals x1 times P1 degree plus x2 times P2 degree. The vapor composition follows by dividing each partial pressure by that total, so y1 equals P1 over P and y2 equals P2 over P. Students use the construction for homework on ideal benzene-toluene style mixtures, phase diagrams, and first VLE estimates; lab instructors check manometer readings against the same closed form; process engineers screen distillations and storage emissions before running a full activity-coefficient package. This calculator accepts both liquid mole fractions and both pure vapor pressures, returns partial pressures, total vapor pressure, vapor mole fractions, unit labels, and the formula string for audit, and rejects mole fractions outside zero to one or a sum that exceeds one so a non-physical composition never becomes a silent scaled pressure.
How two-component Raoult's law defines total vapor pressure
Start from the ideal-solution statement taught in general and physical chemistry for a binary liquid of two volatile species. The partial vapor pressure of component one equals its liquid mole fraction times the pure-component vapor pressure at the same temperature, written P1 equals x1 times P1 degree. The same rule applies to component two: P2 equals x2 times P2 degree.
Under Raoult's law the total vapor pressure above the mixture is simply the sum of those partial pressures, so P total equals x1 times P1 degree plus x2 times P2 degree. Additionally the sum x1 plus x2 must not exceed one, because a liquid composition whose mole fractions exceed one cannot describe a real mixture; the calculator rejects that case rather than inventing a total pressure.
Pure vapor pressures P1 degree and P2 degree are non-negative numbers in any consistent pressure unit you choose for the problem—torr, millimeters of mercury, kilopascals, bar, or atmospheres—and the products and sum are returned in that same unit without conversion. When the total pressure is positive the vapor mole fractions follow as y1 equals P1 over P and y2 equals P2 over P, recovering the ideal VLE composition at that temperature.
Where two-component Raoult calculators show up in real work
Secondary-school and introductory university chemistry courses assign ideal binary vapor-pressure drills that multiply each pure vapor pressure by a stated liquid mole fraction and sum the products; a single trusted oracle speeds grading and demo setup without hand-waving floating-point noise. Laboratory courses measure total vapor pressure of benzene-toluene style mixtures or aqueous-organic pairs and compare experimental manometer readings to the ideal Raoult prediction, so students need the same closed form their report cites.
Process and formulation engineers estimate total pressure and vapor composition for ideal or near-ideal binary storage tanks, flash separators, and first-pass distillation material balances before invoking a full activity-coefficient package. Environmental and occupational-hygiene workflows convert liquid composition into expected partial and total pressures for two volatile organics under the ideal-solution assumption as a first-order screen.
If you later need single-solvent vapor-pressure lowering with a non-volatile solute, multi-component Raoult sums beyond two species, Antoine-based pure vapor pressures from temperature, or boiling-point calculations, treat those as separate search intents and landings rather than overloading this Raoult's law two-component calculator page.
What you can do with it
Homework and exam answer keys
Compute P = x1·P1° + x2·P2° and vapor mole fractions for textbook ideal-binary sets so students and auto-graders share one closed-form ground truth.
Lab binary VLE checks
Predict ideal total vapor pressure and partial pressures from measured liquid mole fractions before comparing to experimental manometer or headspace data.
Process screening of ideal binaries
Estimate total pressure and vapor composition for near-ideal two-component storage, flash, or distillation first-pass sizing without a full thermo package.
FAQ
What is Raoult's law for two components?
For an ideal binary mixture of two volatile liquids, each partial pressure is Pi = xi·Pi° and the total vapor pressure is P = x1·P1° + x2·P2°. Vapor mole fractions follow as yi = Pi / P when P > 0.
What happens if a mole fraction exceeds one?
Each mole fraction must lie in [0, 1], and the sum x1 + x2 must not exceed 1; non-physical compositions are rejected rather than scaled.
Must x1 + x2 equal exactly one?
The sum must be at most one. A sum of one is the usual closed binary liquid; a sum below one is accepted (for example when reporting only two volatile species), but a sum above one fails.
How do I format the input?
0.4, 0.6, 92, 35). Use the same pressure unit for both pure vapor pressures.
What does it cost?
The browser tool is free and runs locally.
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/raoult-two-component \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"mole_fraction_1":0.4,"mole_fraction_2":0.6,"pure_vapor_pressure_1":92,"pure_vapor_pressure_2":35}'const res = await fetch("https://api.kit.forhosting.com/chem/raoult-two-component", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"mole_fraction_1": 0.4,
"mole_fraction_2": 0.6,
"pure_vapor_pressure_1": 92,
"pure_vapor_pressure_2": 35
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/raoult-two-component",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"mole_fraction_1": 0.4,
"mole_fraction_2": 0.6,
"pure_vapor_pressure_1": 92,
"pure_vapor_pressure_2": 35
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/raoult-two-component", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"mole_fraction_1":0.4,"mole_fraction_2":0.6,"pure_vapor_pressure_1":92,"pure_vapor_pressure_2":35}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"mole_fraction_1":0.4,"mole_fraction_2":0.6,"pure_vapor_pressure_1":92,"pure_vapor_pressure_2":35}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/raoult-two-component", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"mole_fraction_1": 0.4,
"mole_fraction_2": 0.6,
"pure_vapor_pressure_1": 92,
"pure_vapor_pressure_2": 35
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.raoult_two_component",
"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
How two-component Raoult's law defines total vapor pressure
Each liquid mole fraction is a dimensionless quantity that must lie in the closed interval from zero to one inclusive; values below zero or above one are non-physical and fail validation with a clear invalid_input message that mole fractions must stay between zero and one. The capability evaluates the closed form in deterministic floating-point arithmetic: no random seeds, no wall-clock timestamps, no network calls, and no model drift, so identical inputs always produce identical JSON. It does not look up Antoine coefficients, convert pressure units, compute bubble or dew points, or sum more than two volatile components; those are separate search intents with their own landings when product coverage grows.
What you send and what you get back
Classic textbook checks include an ideal binary with x1 equals zero point four, x2 equals zero point six, P1 degree around ninety-two and P2 degree around thirty-five yielding partial pressures of about thirty-six point eight and twenty-one and a total near fifty-seven point eight in the same pressure unit, pure-component limits with one mole fraction equal to one and the other zero recovering the corresponding pure vapor pressure exactly, and equal mole fractions with equal pure pressures recovering that pure pressure as the total. Send four required finite numbers under the fields mole_fraction_1, mole_fraction_2, pure_vapor_pressure_1, and pure_vapor_pressure_2. mole_fraction_1 and mole_fraction_2 are the liquid mole fractions x1 and x2; each must lie in the closed interval from zero to one inclusive, and their sum must be at most one. pure_vapor_pressure_1 and pure_vapor_pressure_2 are P1 degree and P2 degree of the pure components at your temperature and must each be non-negative; zero is the non-volatile pure-component limit for that species. Missing fields, non-numeric strings, NaN, Infinity, mole fractions outside zero to one, a sum of mole fractions that exceeds one, and negative pure vapor pressures fail with invalid_input and are not charged. On success the response echoes the cleaned mole fractions and pure vapor pressures, provides partial_pressure_1 and partial_pressure_2 as the Raoult products, total_vapor_pressure as their sum, vapor_mole_fraction_1 and vapor_mole_fraction_2 when the total is positive, mole_fraction_sum, a units hint object, method raoults_law_two_component, and the formula string so homework write-ups can cite the same expression. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where two-component Raoult calculators show up in real work
Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.