Use this chemistry calculator to reproduce a named relationship with explicit quantities and units for study, laboratory planning, or an independent numerical check.

Second-order rate constant (1/(M·s))

Required number input.

Excess reactant concentration (mol/L)

Required number input.

Compute the observed pseudo first order rate constant for a second order reaction with one reactant in large excess. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Observed rate constant (1/s)

The resulting observed rate constant returned as a number.

• Kinetic results assume the selected rate law and constant conditions over the calculation interval. Reaction order, catalyst state, mixing, temperature, competing pathways, and transport limitation must be established independently.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check units and significant figures, compare the result with limiting cases, and use measured or source-specific constants where available. Laboratory, safety, and regulatory decisions require validated methods and appropriate uncertainty analysis.

• First Order Half-Life

  Compute the half-life of a first order reaction as the natural logarithm of two divided by the rate constant.

• Van't Hoff K2

  Compute the natural log of an equilibrium constant at a second temperature with the van 't Hoff relation from the reaction enthalpy and a known value at a first temperature.

• Second Order Half-Life Calculator

  Compute the second-order half-life t½ = 1/(k·[A]₀) from a rate constant and initial concentration.