© Ultrafast Systems LLC /Vernier Software & Technology
18
5.5 The
Experimental
Approach
The data that are obtained in a kinetics experiment could look something like those presented in
Figure 5, which shows the change in concentration of reactant A (open circles) and product B (filled
circles) as a function of time; M is the generic species (A or B).
Figure 5:
Concentration time profiles of reactant and product
On the plot you can see a pair of horizontal lines, one blue (at 0.5) and one red (at 0.37). The
blue one is drawn at the point of 50% reaction (half of the initial concentration of A has been converted
into B). By inspection this occurs after an elapsed time of about 28 milliseconds. This represents the
half
life
, or
half time
, of the reaction. The red line is drawn when about 37% of the initial concentration of A
has been converted to B; this represents the reaction
life time
.
5.6
The Relationships Between Rate Constant, Half Life,
and Life Time
First, we shall consider a first order reaction symbolized by
A
products
The rate of this reaction is as written in Equation 9 as
[ ]
[ ]
d A
k A
dt
Ms
-1
