Enthalpy of dilution calculator
Turn a calorimetry reading into a molar enthalpy of dilution: −8.4 kJ measured while diluting 0.2 mol of solute gives −42 kJ/mol, an exothermic dilution. Only the normalizing step is done here, kept simple and exact. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Heat
- -8.4
- Moles
- 0.2
- Enthalpy of dilution
- -42
- Process
- exothermic
The molar enthalpy of dilution, often written Delta H sub dil or Delta H sub dilution, is the enthalpy change when a solution is diluted by adding solvent, expressed per mole of solute present under the stated conditions. In the laboratory you rarely dilute exactly one mole of solute; instead you measure the heat q exchanged during a dilution of known solute amount n and normalize: Delta H sub dil equals q divided by n. A negative result means the dilution is exothermic—heat is released to the surroundings, common for strong acids and some concentrated salt solutions—while a positive result means the process is endothermic and the mixture cools unless heat is supplied. This calculator takes those two finite numbers—heat and moles—returns the molar enthalpy of dilution with a clear thermal process label, and rejects zero moles because dividing by zero would invent a meaningless molar quantity. Keep energy units consistent: if q is in kilojoules then Delta H sub dil is in kilojoules per mole; if q is in joules the answer is joules per mole.
How molar enthalpy of dilution is defined and computed
Start from a dilution experiment in which solvent—usually water—is added to a concentrated solution under constant-pressure conditions that approximate the thermal process of interest. Calorimetry or an equivalent heat measurement gives the heat q associated with that event for a known amount of solute n that remains constant while concentration falls. Chemistry textbooks and data tables report the intensive quantity per mole of solute, so you divide: Delta H sub dil equals q over n.
The sign convention used here is the system convention of chemical thermodynamics: heat absorbed by the diluting system is positive (endothermic), and heat released to the surroundings is negative (exothermic). Concentrated sulfuric acid diluted carefully into water is a classic exothermic case students meet early; some salts and organic dilutions can be endothermic. The arithmetic is a single division after validating that both fields are finite numbers and that n is strictly greater than zero.
Entries of NaN or Infinity are rejected early. A zero or non-positive mole amount fails with a message that molar enthalpy of dilution is undefined when n equals zero, so clients can fix the stoichiometry rather than receiving Infinity or a silent NaN.
Optional downstream work such as converting grams to moles, planning the volume of water to add, or running multi-step serial dilutions belongs in separate tools; this page stays focused on the normalizing step that students and lab notebooks actually ask for by name when they search for an enthalpy of dilution calculator.
What you send and what you get back
Send two fields. The field heat is a finite number for the heat q exchanged during dilution, in any consistent energy unit such as joules or kilojoules. Use the system sign: negative when heat is released (exothermic dilution), positive when heat is absorbed.
The field moles is a finite positive number for the amount of solute present in moles—the same n before and after dilution if no precipitation occurs. Both fields are required. Classic textbook checks include releasing eight point four kilojoules while diluting a sample that contains zero point two moles of solute to obtain negative forty-two kilojoules per mole (exothermic), and absorbing twelve point six kilojoules with zero point three moles to obtain positive forty-two kilojoules per mole (endothermic).
Keep the same energy unit family throughout a problem set so students never mix joules per mole with kilojoules per mole on the same line of working.
Where enthalpy of dilution calculators show up in real work
Secondary-school and college general chemistry courses constantly assign enthalpy of dilution problems that start from a measured calorimeter temperature change converted to heat and a known solute amount; a single trusted oracle that returns Delta H sub dil and the endothermic or exothermic label speeds grading and demo setup. Process chemists and plant engineers record heat loads when dilute intermediate streams are prepared from concentrated stock, and they need a transparent molar value for heat-balance sheets rather than a black-box table lookup alone.
Acid and base handling labs use measured heat and moles of solute to estimate effective molar heats of dilution for student notebooks and safety briefings. Quality labs that already know q from instrument software still need a deterministic divide-and-label step for LIMS exports and CAPA reports when batch dilution amounts change.
If you later need only the volume of water to reach a target concentration, multi-step serial dilution factors, or molar heat of solution for dissolving a solid solute, treat those as separate search intents and landings rather than overloading this enthalpy of dilution calculator page.
What you can do with it
Homework and exam answer keys
Convert measured dilution heat and moles of solute into ΔH_dil with an endothermic or exothermic label for consistent grading.
Lab notebook normalization
Turn calorimeter heat and weighed moles of solute into a molar enthalpy of dilution for reports and heat-balance sheets.
Process and safety demos
Show students why diluting concentrated acids releases heat from the sign and magnitude of ΔH_dil = q/n for stock solutions.
FAQ
What is the molar enthalpy of dilution?
It is the enthalpy change when a solution is diluted, expressed per mole of solute. From an experiment you compute ΔH_dil = q / n, where q is the heat exchanged and n is the moles of solute present.
How do I know if dilution is endothermic or exothermic?
Negative means exothermic (heat released)—common for strong acids.
What does it cost?
The browser tool is free and runs locally.
What happens if the amount of solute is zero?
The calculation is refused with a clear message, because a heat per mole is undefined when there are no moles. You see the problem in your data straight away instead of an infinite or empty result.
Which unit does the result come out in?
The energy unit of your heat, per mole of solute. Heat in kilojoules gives kilojoules per mole, and heat in joules gives joules per mole, so the result follows whatever your calorimeter reported.
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/enthalpy-dilution \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"heat":-8.4,"moles":0.2}'const res = await fetch("https://api.kit.forhosting.com/chem/enthalpy-dilution", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"heat": -8.4,
"moles": 0.2
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/enthalpy-dilution",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"heat": -8.4,
"moles": 0.2
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/enthalpy-dilution", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"heat":-8.4,"moles":0.2}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"heat":-8.4,"moles":0.2}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/enthalpy-dilution", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"heat": -8.4,
"moles": 0.2
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.enthalpy_dilution",
"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 molar enthalpy of dilution is defined and computed
If the measured heat is essentially zero within floating-point noise, the calculator labels the process thermal_neutral rather than inventing a direction. There is no random seed, no wall-clock timestamp, no network call, and no model drift, so identical heat and moles always produce identical JSON.
What you send and what you get back
Missing fields, empty strings, non-numeric strings, NaN, Infinity, and non-positive moles fail with invalid_input and are not charged. When moles is zero the request fails with a clear message that Delta H sub dil equals q over n is undefined for n equals zero. On success the response echoes the cleaned heat and moles, the molar enthalpy of dilution enthalpy_of_dilution, a process label of endothermic, exothermic, or thermal_neutral, the unit string energy per mol reminding you to keep energy units consistent with your choice of q, the formula string Delta H sub dil equals q over n, and the method enthalpy_dilution. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where enthalpy of dilution 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.
Technical questions
What happens if moles is zero?
The request fails with invalid_input. Molar enthalpy of dilution is undefined when n = 0 because the formula divides by the amount of solute.
What units should I use?
Keep energy units consistent. If heat is in kJ, enthalpy_of_dilution is in kJ/mol; if heat is in J, the answer is in J/mol. moles must be in mol.