Half-Life Calculator (Chemical)

The half-life of a substance is the time it takes for half of it to decay or break down — a concept used in chemistry, pharmacology, and nuclear science. The Half-Life Calculator solves for any one of four variables: select what you want to calculate (Remaining Quantity, Half-Life, Initial Quantity, or Time Elapsed), then enter the known values and your time unit to get the result. Secondary outputs include the Decay Constant (λ), Mean Lifetime (τ), and Percentage Remaining.

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Results

Result

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Decay Constant (λ)

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Mean Lifetime (τ)

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Percentage Remaining

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Frequently Asked Questions

What is radioactive decay?

Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. During this process, the nucleus transforms into a different element or isotope, releasing particles and energy in the form of radiation.

How is half-life related to decay constant?

Half-life and decay constant are inversely related. The decay constant (λ) represents the probability of decay per unit time, while half-life (T½) is the time needed for half the sample to decay. They're related by: λ = ln(2)/T½.

What is the difference between half-life and mean lifetime?

Half-life is the time for half a sample to decay, while mean lifetime is the average time a particle exists before decaying. Mean lifetime (τ) equals 1/λ, where λ is the decay constant, and is about 1.44 times longer than the half-life.

Can this calculator be used for chemical reactions?

Yes, this calculator works for any first-order decay process, including chemical reactions that follow exponential decay kinetics. It's commonly used for radioactive decay, drug metabolism, and certain chemical decomposition reactions.

What is carbon-14 dating and its half-life?

Carbon-14 dating uses the radioactive decay of carbon-14 to determine the age of organic materials. Carbon-14 has a half-life of approximately 5,730 years, making it useful for dating materials up to about 50,000 years old.

How accurate are half-life calculations?

Half-life calculations are very accurate when the decay follows first-order kinetics and measurement conditions are controlled. However, real-world factors like temperature, pressure, and sample purity can affect actual decay rates.