Meia-vida ordem 2
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The second-order half-life calculator helps determine the time required for the concentration of a reactant to reduce by half. For reactions of the type A → products, the half-life (t½) depends on the rate constant (k) and the initial concentration ([A]₀) of the reactant, according to the formula t½ = 1/(k·[A]₀). Unlike first-order reactions, where half-life remains constant, this formula shows an inverse relationship with the initial concentration.
This tool is useful in chemical kinetics for predicting degradation times in experiments or industrial processes. Practical examples include studying the decomposition of hazardous compounds or analyzing drug stability. To use it correctly, confirm the reaction follows second-order kinetics and ensure initial concentration units match the rate constant's requirements.
Important considerations: the formula applies only to single-reactant reactions (A → products) or when one reactant is in excess. For multiple reactants with varying concentrations, a different approach is needed. Also, ensure the rate constant (k) is expressed in L·mol⁻¹·s⁻¹ to avoid calculation errors.
Frequently asked questions
How does second-order half-life differ from first-order?
In first-order, half-life is constant and independent of initial concentration. In second-order, it varies inversely with [A]₀ using t½ = 1/(k·[A]₀).
Can I use this calculator for two-reactant reactions?
Only if one reactant is in excess. For 2A → products or A + B → products, different formulas are required.
What happens if I use incorrect units for k?
The result will be wrong. The second-order rate constant k must be in L·mol⁻¹·s⁻¹. Convert units before calculation.
Why are half-lives important in chemical kinetics?
They help predict substance stability or the time needed to reduce concentrations in industrial and environmental processes.