Online Tool Store
Reaction Rate Calculator
Compute remaining concentration, half-life and instantaneous rate for zero, first and second order kinetics, plotted on a chart with a shareable link.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Rate = 0.0500 × [A]
Remaining Concentration [A]ₜ
Reaction Half-Life (t₁/₂)
Instantaneous Rate at time t
M · s⁻¹
Concentration [A] vs. Time
How it works
- Select the reaction kinetics order (Zero Order, First Order, or Second Order).
- Enter the chemical rate constant (k) and the starting reactant concentration [A]₀ in Molar (M).
- Specify the elapsed reaction duration in seconds, minutes, or hours.
- The calculator computes the remaining concentration [A]ₜ, percentage reacted, half-life (t₁/₂), and instantaneous reaction rate, plotted on a concentration-vs-time chart.
- Copy the result as text, or copy a share link that reopens the calculator with this exact setup.
The formula
Zero Order: [A]ₜ = [A]₀ − kt | t₁/₂ = [A]₀ / (2k)
First Order: ln[A]ₜ = ln[A]₀ − kt | t₁/₂ = ln(2) / k
Second Order: 1/[A]ₜ = 1/[A]₀ + kt | t₁/₂ = 1 / (k[A]₀)
FAQ
What is reaction order in chemical kinetics?
Reaction order defines how the chemical reaction rate depends on the concentration of reactants. Zero-order reactions proceed at a constant rate independent of concentration; first-order reaction rates are linearly proportional to [A]; and second-order rates are proportional to the square of concentration [A]².
Why is first-order half-life constant?
For a first-order chemical reaction, the integrated rate law yields t₁/₂ = ln(2) / k ≈ 0.693 / k. Because the initial concentration [A]₀ cancels out of the equation, exactly 50% of the remaining reactant decays in every successive half-life period.
What are the units of the rate constant (k)?
The units of k depend on the overall reaction order: M·s⁻¹ (molarity per second) for zero order, s⁻¹ (reciprocal seconds) for first order, and M⁻¹·s⁻¹ for second order.
How do integrated rate laws differ from differential rate laws?
A differential rate law expresses the instantaneous speed of a reaction as a function of current concentration (Rate = −d[A]/dt = k[A]ⁿ), while an integrated rate law expresses reactant concentration as a direct function of elapsed time t.
What does it mean if the rate constant (k) is zero?
k = 0 means the reaction isn't proceeding at all — concentration stays at [A]₀ forever, so the half-life is infinite (shown as "∞"). It's a valid input, not an error: the calculator now shows this explicitly instead of a broken result.
How do I calculate a rate constant for a first-order reaction?
Rearrange the integrated first-order rate law: k = ln([A]₀ / [A]ₜ) / t. If you instead know the half-life, k = ln(2) / t₁/₂ ≈ 0.693 / t₁/₂. This calculator solves the forward direction (concentration and half-life from a known k); solving for k from two measured concentrations is a natural follow-up we've noted for a future pass.
How we compare
| Feature | Online Tool Store | CalcBE's kinetics calculator | Omni Calculator's rate constant tool |
|---|---|---|---|
| Integrated rate laws for 0th, 1st, and 2nd order | ✓ | ✓ | ✓ |
| Instant half-life & % consumption breakdown | ✓ | ✓ | Half-life only, no % consumed |
| Concentration-vs-time chart | ✓ | ✓ | ✗ |
| Copy a share link with your exact inputs | ✓ | ✓ | ✓ |
| Clear error state for invalid inputs (k < 0, [A]₀ ≤ 0) | ✓ | Not shown | Not shown |
| Multi-unit elapsed time (sec, min, hr) | ✓ | Consistent units required, no converter | ✓ (sec, min, hr for k's time basis) |