Half-life: Difference between revisions

From Citizendium
Jump to navigation Jump to search
imported>Robert W King
No edit summary
imported>David E. Volk
No edit summary
Line 1: Line 1:
{{subpages}}
{{subpages}}
'''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-life''' 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]] (CH<sub>3</sub>N=NCH<sub>3</sub>) into methane and nitrogen gasMany 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.


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]] (CH<sub>3</sub>N=NCH<sub>3</sub>) 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 ==


== Mathematics ==
The future concentration of a substance, C<sub>1</sub>, after some passage of time <math>\Delta</math>T, can easily be calculated if the present concentration, C<sub>0</sub>, and the half-life, T<sub>h</sub>, are known:


The future concentration of a substance, C1, after some passage of time  <math>\Delta</math>T, can easily be calculated if the present concentration, C0, and the half-life, T1/2, are known:
:<math>C_1 = C_0  x e^\frac{\Delta_T}{T_h}</math>

Revision as of 14:48, 25 April 2008

This article is a stub and thus not approved.
Main Article
Discussion
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
 
This editable Main Article is under development and subject to a disclaimer.

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-life 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, Th, are known: