What it does
How fast a reaction goes depends on how much reactant is left, and the way it depends is the order of the reaction. This page draws what each order looks like.
- Three graphs. Choose zero, first or second order and set the starting concentration [A]₀ and the rate constant k. The page plots [A], ln[A] and 1/[A] against time. Only one of the three is a straight line: [A] for zero order, ln[A] for first order and 1/[A] for second order. That graph is outlined and marked “straight”, and its slope is given.
- Half-lives. Dotted lines on the [A] graph mark each successive half-life. For first order they are evenly spaced; for second order each is twice as long as the last; for zero order each is half as long, and [A] reaches zero at a definite time.
- Formulas. The rate law, the integrated rate law and the half-life, with your numbers filled in.
- Temperature and catalysts. Set an activation energy Ea and a temperature T. The page shows k from the Arrhenius equation, how many times faster the reaction is 10 K warmer, the fraction of collisions with enough energy, and an energy profile. Tick the catalyst and a second, lower hump appears: Ea drops, ΔH does not change, and k goes up.
It follows Class 12 Chemistry (chemical kinetics: rate of a reaction, rate law and order, integrated rate equations for zero and first order reactions, half-life, temperature dependence and the Arrhenius equation, the effect of a catalyst, collision theory). To find the order and k from your own measurements, use the reaction kinetics fitter; to see how a catalyst leaves an equilibrium unchanged, try the le Chatelier sandbox sandbox.
How to use it
- Pick the order.
- Move the [A]₀ and k sliders and watch the graphs and the half-life.
- In the second card, move Ea and T, and tick the catalyst.
- Try the Check yourself questions; New questions gives a fresh set.
Worked example: a first-order reaction
First order, [A]₀ = 1 mol/L, k = 0.01 s⁻¹.
- t½ = 0.693 / k = 0.693 / 0.01 = 69.3 s. The page reads “t½ = 69.3 s”.
- After 69.3 s, [A] = 0.5 mol/L; after 138.6 s, 0.25 mol/L; the dotted lines are evenly spaced.
- The ln[A] graph is the straight one, with slope −k = −0.01.
- Change [A]₀ to 2 mol/L: the half-life stays 69.3 s. That is the mark of first order.
Now switch to second order with the same numbers: t½ = 1 / (k[A]₀) = 100 s, and the next half-life is 200 s.
Arrhenius: with Ea = 75 kJ/mol at 300 K, going to 310 K makes the reaction about 2.6 times faster. Ticking the catalyst lowers Ea to 45 kJ/mol, and k rises by a factor of about 170 000.
Tips
- The units of k tell you the order: mol L⁻¹ s⁻¹ (zero), s⁻¹ (first), L mol⁻¹ s⁻¹ (second).
- Radioactive decay is first order, so it has a constant half-life.
- The “doubles every 10 K” rule only holds for Ea near 50 kJ/mol around room temperature.
FAQ
Can a real reaction be zero order? Yes, for example a reaction on a metal surface that is fully covered: adding more gas does not speed it up.
Is anything saved? No. Everything runs in your browser and nothing is stored or sent.
Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.
Where the numbers come from
- Integrated rate laws, half-lives and the Arrhenius equation: general chemistry facts, written fresh for fibub. Gas constant R from CODATA (NIST).
- The pre-exponential factor (10¹¹ s⁻¹) and ΔH (−40 kJ/mol) used to draw the energy profile are example values.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.