The half-life of titanium-44 is 63 years. What is the constant k in the decay formula for the substance?
1 Answer
Explanation:
All you really need to use here is the fact that for a first-order reaction like radioactive decay, the integrated rate law takes the form
#ln(["A"]) - ln(["A"]_0) = - k * t#
Here
#["A"]# is the concentration of the reactant after a given time#t# passes#["A"]_0# is the initial concentration of the reactant#k# is the rate constant
Now, the half-life of a radioactive nuclide,
This means that after the passing of one half-life, you have
#t = t_"1/2"#
and
#["A"] = 1/2 * [A"]_0#
Plug this into the expression of the integrated rate law to get
#ln(1/2 * ["A"]_0) - ln(["A"]_0) = - k * t_"1/2"#
Rearrange to solve for
#ln( (1/2 * color(red)(cancel(color(black)(["A"]_0))))/color(red)(cancel(color(black)(["A"]_0)))) = - k * t_"1/2"#
#ln(1/2) = - k * t_"1/2"#
You can rewrite this as
#ln(1) - ln(2) = - k * t_"1/2"#
which will get you
#k = ln(2)/t_"1/2"#
Finally, plug in the value you have for the half-life of titanium-44 to find
#k = ln(2)/"63 years" = color(darkgreen)(ul(color(black)("0.011 years"^(-1))))#
The answer is rounded to two sig figs.