First-Order Reaction Calculator

In a first-order reaction, the rate at which a reactant breaks down depends directly on its current concentration — a pattern common in radioactive decay, pharmacokinetics, and chemical kinetics. Enter your Initial Concentration [A₀], Rate Constant (k), and Time (t) into the First-Order Reaction Calculator, then select what to calculate. You'll get the Final Concentration [A], along with Reaction Rate, Half-Life, and Percent Remaining as secondary outputs.

mol/L

Starting concentration of the reactant

s⁻¹

First-order rate constant

s

Duration of the reaction

Results

Final Concentration [A]

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Reaction Rate

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Half-Life

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Percent Remaining

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Results Table

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Frequently Asked Questions

How do you calculate first-order reaction concentration?

Use the first-order integrated rate law: [A] = [A₀] × e^(-kt), where [A] is final concentration, [A₀] is initial concentration, k is the rate constant, and t is time.

What is the rate equation for a first-order reaction?

The rate equation is: rate = k[A], where the reaction rate is directly proportional to the concentration of one reactant raised to the first power.

How do you find the half-life of a first-order reaction?

For first-order reactions, half-life is constant and calculated as: t₁/₂ = ln(2)/k = 0.693/k, where k is the rate constant.

What factors affect the rate constant in first-order reactions?

The rate constant depends on temperature (following Arrhenius equation), catalyst presence, and the nature of reactants. It's independent of concentration in first-order kinetics.

How is first-order kinetics different from zero-order?

In first-order reactions, the rate depends on reactant concentration, while zero-order reactions have constant rates independent of concentration. First-order shows exponential decay.

What are common examples of first-order reactions?

Radioactive decay, decomposition of N₂O₅, hydrolysis of sucrose, and many organic substitution reactions follow first-order kinetics.