Half-life
'This article is about decomposition. For other uses of the term "Half-life", please see Half-life (disambiguation. For any reactant subject to first-order decomposition, the amount of time needed for one half of the substance to decay is referred to as the half-live of that compound. Although the term is often associated with radioactive decay, it also applies equally to chemical decomposition, such as the decomposition of azomethane (CH3N=NCH3) into methane and nitrogen gas. Many compounds decay so slowly that it is impractical to wait for half of the material to decay to determine the half-life. In such cases, a convenient fact is that the half-life is 693 times the amount of time required for 0.1% of the substance to decay. Using the value of the half-life of a compound, one can predict both future and past quantities.
Mathematics
The future concentration of a substance, C1, after some passage of time T, can easily be calculated if the present concentration, C0, and the half-life, T1/2, are known:
