Sodium-24 has a half life of 15 hours. Suppose you had a sample containing 0.010 moles of Na-24. How many hours would be required to reduce your sample to 6.25x10^-4 moles

Answer : The time required would be, 60.0 hours

Explanation :

Half-life = 15 hr

First we have to calculate the rate constant, we use the formula :

Now we have to calculate the time passed.

Expression for rate law for first order kinetics is given by:

where,

k = rate constant  =

t = time passed by the sample  = ?

a = initial amount of the reactant  = 0.010 mol

a - x = amount left after decay process = 6.25 × 10⁻⁴ mol

Now put all the given values in above equation, we get

Therefore, the time required would be, 60.0 hours