Posted by Confused on .
The rate of the following reaction:
Radioactive decay of 90Sr,
is characterized by the rate constant k = 0.024 year1. What is the halflife (in years) for this reaction at the same conditions when the initial concentrations are 0.0356 M? (Round your answer to 3 significant figures.)
Hint: The units of the rate constant are linked with the order of reaction.
Answer:________________years

Concentration and Reaction 
DrBob222,
Radioactive decay is a first order reaction. t_{1/2} = 0.693/k
Solve for t_{1/2}.
It doesn't matter that conditions are changed, the halflife is the same; half life of first order reactions don't depend upon the initial concn. You can show that, however, by using
ln(No/N) = kt
Substitute 0.0356 M for No and half that for N and 0.024 for k. t_{1/2} will be the same as obtained by 0.693/0.024.