Select reaction order and enter two data points.
The rate constant k quantifies reaction speed. Its value and units depend on reaction order: Zero order: [A] = [A]₀ − kt, k in M/s, t½ = [A]₀/(2k). First order: ln[A] = ln[A]₀ − kt, k in s⁻¹, t½ = ln2/k (independent of concentration). Second order: 1/[A] = 1/[A]₀ + kt, k in M⁻¹s⁻¹, t½ = 1/(k[A]₀). To determine order experimentally: plot [A] vs t (linear → 0th), ln[A] vs t (linear → 1st), 1/[A] vs t (linear → 2nd). Temperature dependence follows the Arrhenius equation: k = Ae^(−Ea/RT). Catalysts increase k by lowering activation energy. Rate constants are essential for reactor design, drug metabolism prediction, and environmental pollutant degradation modeling.