# Reaction Rate Constant Calculator

Free rate constant calculator for zero, first, and second order reactions. Calculate rate, k, or concentration with step-by-step solutions.

## What this calculates

Calculate the reaction rate, rate constant (k), or reactant concentration for zero, first, and second order reactions. Select the reaction order and solve for any unknown variable.

## Inputs

- **Reaction Order** — options: Zero Order: rate = k, First Order: rate = k[A], Second Order: rate = k[A]² — Select the order of the reaction.
- **Solve For** — options: Reaction Rate, Rate Constant (k), Concentration [A] — Select what to calculate.
- **Rate Constant (k)** — min 0 — The rate constant k. Units depend on reaction order.
- **Concentration [A]** (mol/L) — min 0 — Concentration of reactant A in mol/L.
- **Reaction Rate** (mol/(L·s)) — min 0 — Rate of reaction in mol/(L·s).

## Outputs

- **Result** — formatted as text — The calculated value with units.
- **Rate** — Reaction rate in mol/(L·s).
- **Rate Constant Units** — formatted as text — Units of k for the given reaction order.
- **Calculation** — formatted as text — Step-by-step calculation.

## Frequently Asked Questions

**Q: What is a rate constant?**

A: The rate constant (k) is a proportionality constant in the rate law that relates reaction rate to reactant concentrations. Its value depends on temperature and the specific reaction, but not on concentrations.

**Q: How does temperature affect the rate constant?**

A: The rate constant increases with temperature, typically doubling for every 10°C rise. The Arrhenius equation describes this: k = A·exp(-Ea/RT). See the activation energy calculator for details.

**Q: What determines reaction order?**

A: Reaction order is determined experimentally by measuring how the rate changes when concentrations are varied. It is NOT determined from the balanced equation coefficients (except for elementary reactions).

**Q: What are the units of k?**

A: Units of k depend on overall order: zero order = mol/(L·s), first order = s⁻¹, second order = L/(mol·s). The units ensure the rate always comes out in mol/(L·s).

---

Source: https://vastcalc.com/calculators/chemistry/rate-constant
Category: Chemistry
Last updated: 2026-04-21