Entropy change calculator
Absorbing 1,000 J of heat at 300 K raises a system's entropy by about 3.33333333333 J/K. Enter the heat and the absolute temperature, and the result follows ΔS = Q/T, with a clear warning if the temperature is not above zero kelvin. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Heat energy transferred
- 1,000
- Creativity
- 300
- Entropy change
- 3.3333333333 J/K
Entropy change quantifies how heat flow at a given absolute temperature redistributes the availability of energy in a thermodynamic system. In the reversible constant-temperature model used throughout introductory physics and engineering thermodynamics, the entropy change of a system that absorbs or rejects heat Q at absolute temperature T is simply Delta S equals Q divided by T, with SI units of joules per kelvin. This calculator accepts the heat transferred in joules and the absolute temperature in kelvin, validates that temperature is strictly positive, then returns the entropy change with cleaned inputs, unit labels, and the defining formula string. Non-positive temperatures are rejected with a clear validation error because the absolute scale cannot be zero or negative and the ratio would be undefined or unphysical.
How entropy change is defined from heat and absolute temperature
Start from the reversible heat-transfer idealization taught in first-year thermodynamics: when a system exchanges heat Q with a thermal reservoir held at constant absolute temperature T, the entropy change of the system is Delta S equals Q divided by T. Heat Q is energy in joules; temperature T must be on an absolute scale in kelvin because the definition is rooted in the absolute thermodynamic temperature that appears in the second law.
Positive Q means the system absorbs heat and its entropy rises; negative Q means the system rejects heat and its entropy falls. The calculator does not integrate dQ reverse over T along a multi-step path with varying temperature, does not add irreversible entropy generation terms for friction or free expansion, and does not look up tabulated material properties. It answers only the algebraic definition Delta S equals Q over T that problem sets and design hand-checks use when temperature is treated as constant.
Where entropy change calculations show up in real work
Secondary-school and college physics courses constantly assign isothermal heat-transfer problems that give Q and T and ask for Delta S of the system, the surroundings, or both. University engineering thermodynamics courses use the same two-number reduction before they introduce path integrals, Clausius inequality, and availability analysis. Process engineers sanity-check isothermal exchangers and condensers by converting measured heat duty and stream temperature into entropy flow for second-law efficiency estimates.
HVAC designers compare entropy production across cooling coils when only heat rejected and absolute temperature are known from sensor data. If you later need variable-temperature path integrals of dQ over T, irreversible generation accounting, unit conversion between Celsius and kelvin as a dedicated landing, or a material property lookup, treat those as separate search intents rather than overloading this entropy change calculator page.
What you can do with it
Homework and exam answer keys
Compute ΔS = Q/T for isothermal heat-transfer problems so teachers and auto-graders share one SI ground truth including non-positive temperature rejection.
Isothermal process design checks
Convert measured heat duty and absolute stream temperature into entropy change for condensers, evaporators, and isothermal compressors.
Second-law teaching demos
Show system versus surroundings entropy for reversible heat exchange at fixed T without running a full cycle simulator.
FAQ
What happens if temperature is zero or negative?
Absolute temperature must be strictly positive; ΔS = Q/T is undefined or unphysical for T ≤ 0.
What units should I use?
The result is in J/K. Convert °C to kelvin (add 273.15) before calling if your data are in Celsius.
What does it cost?
The browser tool is free and runs locally.
Can the heat value be negative?
Yes. A negative heat value means the system releases heat, so the entropy change comes out negative and the system's entropy falls. A positive value means heat absorbed and entropy rising.
Does it work if the temperature changes during the process?
No. It applies ΔS = Q/T at one constant temperature, as in isothermal textbook problems. A process whose temperature varies needs the step-by-step integral of heat over temperature, which this calculator does not do.
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/thermo/entropy-change \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"heat_transferred":1000,"temperature":300}'const res = await fetch("https://api.kit.forhosting.com/thermo/entropy-change", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"heat_transferred": 1000,
"temperature": 300
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/thermo/entropy-change",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"heat_transferred": 1000,
"temperature": 300
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/thermo/entropy-change", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"heat_transferred":1000,"temperature":300}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"heat_transferred":1000,"temperature":300}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/thermo/entropy-change", 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_transferred": 1000,
"temperature": 300
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "thermo.entropy_change",
"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 entropy change is defined from heat and absolute temperature
The critical validation edge is temperature: if T is zero, negative, or vanishes within floating-point epsilon, the request fails with invalid input instead of returning Infinity, NaN, or a meaningless finite number.
What you send and what you get back
When temperature is zero or negative the error message states that entropy change cannot be computed for non-positive absolute temperature, so clients can correct unit mistakes such as forgetting to convert Celsius to kelvin. Classic textbook checks include one thousand joules absorbed at three hundred kelvin, which yields about three point three three three joules per kelvin; heat rejected during isothermal compression of an ideal gas; and cooling loads where Q is negative. Wire the free browser form for homework and lab write-ups, then call the identical contract from scripts when you need bulk answer keys or automated grading. Send two finite numbers under the fields heat_transferred and temperature. heat_transferred is Q in joules and may be positive or negative depending on whether heat enters or leaves the system. temperature is absolute T in kelvin and must be strictly greater than zero. Missing fields, non-numeric strings, NaN, and Infinity fail with invalid_input and are not charged. On success the response echoes cleaned inputs, entropy_change as Delta S in joules per kelvin, a unit string of J/K, the formula string, and method entropy_change. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance and return a structured error code that clients can map to form messages.
Where entropy change calculations 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 formula does this entropy change calculator use?
ΔS = Q / T, where Q is heat_transferred in joules and T is absolute temperature in kelvin. The result is entropy_change in J/K.
Can heat_transferred be negative?
Yes. Negative Q means heat leaves the system and yields a negative entropy change for the system under this reversible model.