Chemistry

Chemistry for medical professionals

Chemistry for medical professionals



We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Half-life in 1st order reactions

The half-life can be calculated from the law of speed. Again we consider a simple reaction:

A.B.

These reactions take place in the 1st order:

d[A.]dt=k[A.]

By changing (variable separation) one obtains:

d[A.][A.]=kdt

The equation is now integrated, with the starting situation before the start of the reaction being chosen as the zero point. [A.]0 denotes the initial concentration of A at t = 0.

[A.]0[A.]d[A.][A.]=0tkdt

It follows:

ln([A.][A.]0)=kt

This equation applies to the entire course of a first-order reaction. We now consider the half-life t½. After a half-life, the concentration of A has decreased by half: [A] = ½[A.]0. This is now plugged into the equation, [A.]0 can be shortened.

ln(12[A.]0[A.]0)=ln(12)=kt½

It applies ln(1/2)=-ln(2). By transformation we get an expression for the half-life:

Half-life
t½=ln(2)k

The half-life is therefore independent of the concentration of the educt. This is characteristic of first-order reactions. Radioactive decay also obeys a rate law 1. This is used when determining the age, for example using the C14 method.


Video: Læger tigger om ikke at spise + disse 12 kræftfremkaldende fødevarer! (August 2022).