Reaction rate calculator
A concentration change of 0.5 mol/L over 10 s is an average rate of 0.05 mol/L per second. Enter the change in concentration and the elapsed time to get the signed rate, its magnitude and each substitution step. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Concentration change
- 0.5
- Time
- 10
- Delta c
- 0.5
- Delta t
- 10
- Average rate
- 0.05
- Interest rate
- 0.05
A reaction rate calculator turns a measured concentration change and an elapsed time into the average rate used in kinetics homework, lab reports, and automated checks. Enter how much concentration changed over the interval and how long that interval lasted; the tool returns average rate equals delta c over delta t, the absolute magnitude of that rate, a readable formula, and step-by-step substitution so you can verify the arithmetic by hand.
What average reaction rate means
Average reaction rate over a time interval is the change in concentration of a species divided by the elapsed time of that interval. In symbols, average rate equals delta c over delta t, where delta c is the final concentration minus the initial concentration of the tracked species and delta t is the duration of the observation. When the tracked species is a product, delta c is typically positive and the signed rate is positive.
When the tracked species is a reactant that is consumed, delta c is negative and the signed rate is negative; many worksheets then report the magnitude of the rate so that every reported rate is non-negative. Classroom kinetics problems, quality-control sampling logs, and introductory physical-chemistry exercises all rely on this closed definition. The tool implements that formula only: it does not fit zero-order, first-order, or second-order integrated rate laws, does not estimate instantaneous rates from multiple samples, and does not convert between concentration or time units.
When elapsed time is zero or near-zero the ratio is undefined, so the tool rejects the input rather than inventing a rate for a zero-length interval.
Practical tips, limits, and related searches
Keep concentration and time in consistent units before you call the tool; converting moles per litre and seconds yourself is outside the scope of this calculator, and mixing millimoles with hours will produce a numerically valid but dimensionally confusing rate if left inconsistent. Prefer sending numbers rather than pre-formatted strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern.
When concentration does not change, the signed rate is zero and the message says so explicitly so automated tests can assert a flat interval. This landing targets people searching for a reaction rate calculator, average rate from concentration change, or delta c over delta t online; it is not an integrated rate-law fitter, not a half-life tool, and not an Arrhenius calculator.
Prefer this capability when you already have a single interval’s delta concentration and duration and only need the average rate; if your source is a full concentration–time table, pick one interval or pre-compute the deltas first.
What you can do with it
Homework checks for average rate
Students enter Δc and Δt from textbook kinetics problems and compare hand-written average rate and magnitude against a deterministic result before submitting.
Lab notebook interval rates
Technicians log sampled concentration changes over fixed sampling intervals and get a consistent average-rate figure without spreadsheet formulas.
FAQ
How is average reaction rate calculated?
Average rate = concentration change (Δc) divided by elapsed time (Δt).
Does this fit a rate law or half-life?
No. It only computes the average rate for one interval. Use a dedicated kinetics or half-life tool for integrated rate laws.
Is the reaction rate calculator free?
The browser tool is free and runs locally.
Why is my rate negative?
Because you tracked a reactant that is being used up, so its concentration change is negative. The calculator shows that signed rate and, next to it, the magnitude most worksheets report as a positive number.
Can it give the instantaneous rate?
No. It gives the average rate over one interval and does not estimate instantaneous rates from several samples. With a full concentration-time table, pick one interval and enter its change and duration.
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/reaction-rate \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"concentration_change":0.5,"time":10}'const res = await fetch("https://api.kit.forhosting.com/chem/reaction-rate", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"concentration_change": 0.5,
"time": 10
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/reaction-rate",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"concentration_change": 0.5,
"time": 10
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/reaction-rate", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"concentration_change":0.5,"time":10}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"concentration_change":0.5,"time":10}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/reaction-rate", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"concentration_change": 0.5,
"time": 10
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.reaction_rate",
"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.
Limits
max_abs | 1000000000000 |
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
When elapsed time is zero the quotient is undefined, so the API returns a clear invalid_input error instead of Infinity or a silent NaN.
What average reaction rate means
This calculator returns both: the signed average_rate equal to concentration_change divided by time, and abs_rate equal to the absolute value of the concentration change divided by the absolute value of time.
How to call the API and what comes back
Concentration change may be positive or negative; elapsed time must be non-zero—values whose absolute value is at or below one times ten to the minus fifteen are treated as zero and rejected. Send a JSON body with two required finite numbers: concentration_change (aliases delta_c, delta_concentration, change, dc, conc_change, delta_conc) and time (aliases elapsed_time, delta_t, dt, t, duration, time_elapsed). Absolute values must stay within the published limit of one trillion so intermediate quotients remain finite in IEEE double precision on the Worker and in the browser. On success the response echoes rounded concentration_change and time, mirrors them as delta_c and delta_t, sets average_rate and rate to the same rounded signed quotient, abs_rate to the non-negative magnitude, formula to the string average rate equals delta c over delta t, message to a short English summary, and steps to an ordered array of substitution lines. Failed validation—missing fields, non-finite numbers, values outside absolute limits, a non-finite rate, or zero time—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and related searches
For teaching, pair examples: a concentration change of zero point five over ten time units yields an average rate of zero point zero five; a negative reactant change of minus zero point two over four units yields a signed rate of minus zero point zero five with abs_rate zero point zero five; and time zero demonstrates the hard invalid_input path that protects division by zero. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately set time to zero. Round-trip checks are easy: recompute concentration_change divided by time by hand and confirm it equals the published average_rate within the same twelve-decimal rounding, and confirm that abs_rate equals the absolute value of that quotient when time is positive.
Integration use cases
Unit tests for kinetics software
Generate known-good positive, negative, and zero-Δc rates plus deliberate zero-time rejections for coding kata and API contract tests.
Technical questions
What happens when time is zero?
The rate is undefined (division by zero). This tool returns invalid_input instead of Infinity or NaN.
Can concentration change be negative?
Yes. Negative Δc is normal for a reactant being consumed; average_rate keeps the sign, and abs_rate reports the magnitude.