Adecomposition reaction has a rate constant of 0.0012 yr^-1
(a) what is the half-life of the reaction?
(b) how long does it take for [reactant] to reach 15% of its original value?

A) 577.6 years

B) 1580.9 years

Explanation:

You can know the order of a reaction given the units of the rate constant:

Then we know that this is a first order reaction because years is a unit of time as well as seconds. The half life of a first order reaction is given by:

Here you can solve for the half life:

Now for the rate law for a first order reaction is:

Then, if you want to know how long does it take to reach a certain value you solve for time:

The 15% of its original value is

You solve for time:

Hope it helps!

it forms an anion that has a larger radius. anions have a negative charge and are larger than the original atom.