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ChemBench
How fast reactions proceed depends on the order — each has its own integrated rate law and half-life formula.
A zeroth-order reaction consumes reactant at a constant rate regardless of concentration. A first-order reaction (like radioactive decay) has an exponential decay with a constant half-life. A second-order reaction slows down dramatically as concentration drops — each order produces a distinctly different concentration-vs-time curve.
Only first-order reactions have a concentration-independent half-life (t½ = ln2/k) — for zeroth order, half-life depends on initial concentration (t½ = [A]₀/2k), and for second order it depends inversely on concentration (t½ = 1/k[A]₀). This is why radioactive half-lives are constant but chemical half-lives often aren't.
Molar mass of any chemical formula (e.g. H2O, C6H12O6, Ca(OH)2).
OpenPercent composition of an element within a chemical formula.
OpenSimplest whole-number ratio formula from elemental masses or percentages.
OpenPercent yield from actual and theoretical reaction yields.
OpenFinal concentration [A]
0.368 mol/L
What you entered
[A] = [A]₀ × e^(−kt) (first order)
1 × e^(−0.05 × 20)= 0.3679 Mt½ = ln(2) ÷ k
0.6931 ÷ 0.05= 13.8629 sResult
Final [A]: 0.368 mol/L
For a first-order reaction with k = 0.05, after 20 s the concentration drops from 1 to 0.368 mol/L. Half-life = 13.863 s.