# Half-life

A half-life is the time it takes for a substance undergoing decay to decrease by half. The half-life of a substance is a constant, regardless of the amount of substance present.

##### Why is it called Half-Life?

The term "half-life" is used to describe the amount of time it takes for a given quantity of a substance to decay or reduce by half. In the case of the Half-Life video game, the term is used to describe the amount of time it takes for the game's main character, Gordon Freeman, to find and activate a device that will allow him to travel back in time and change the events that led to the game's apocalyptic setting.

### How long is a Half-Life?

A Half-Life is typically defined as the time it takes for half of a given quantity of a substance to decay. For example, the Half-Life of uranium-238 is 4.468 billion years. This means that, after 4.468 billion years, only half of the original quantity of uranium-238 will remain.

##### What is the Half-Life in chemistry?

In general, the half-life (t1/2) of a chemical species is the time required for the concentration of the species to fall to half of its initial value. The half-life is a function of the rate constant (k) of the chemical reaction and the initial concentration (C0) of the reactant. The relationship between the half-life and the rate constant is given by the following equation:

t1/2 = ln(2)/k

For a first-order reaction, the rate constant is simply the inverse of the half-life:

k = 1/t1/2

The half-life of a chemical species can be affected by a number of factors, including temperature, pressure, and the presence of other chemicals ( catalysts or inhibitors).

What happens after a half-life? A half-life is the time it takes for a given quantity of a substance to decay to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay. The half-lives of various radioactive isotopes have been measured and found to be very consistent. For example, the half-life of carbon-14 is 5,730 years. This means that after 5,730 years, only half of the original carbon-14 atoms will remain. After another 5,730 years, only a quarter of the original atoms will remain, and so on.

What does half-life of 12 hours mean? The half-life of a radioactive substance is the time it takes for half of the atoms to decay. This means that if you have a sample of a radioactive substance with a half-life of 12 hours, after 12 hours, half of the atoms will have decayed. After 24 hours, half of the remaining atoms will have decayed, and so on.