A first-order decomposition reaction has a rate constant of 0.00140 yr−1. How long does it take for [reactant] to reach 12.5% of its original value? Be sure to report your answer to the correct number of significant figures.

Explanation:

rate constant k = .00140 yr⁻¹

k is rate constant , t is time taken for  decrease of initial concentration of a to a₁

Here a = 100 , a₁ = 12.5

.00140 = (1 / t )  x  ln 100 / 12.5

.00140 = 2.07944 / t

t = 1485.3 yr .

391.

Step-by-step explanation:

There is 60 minutes every hour, so you divide by 60. 68 / 60 = 1.1333333333.

Now, we have to find out how many minutes there are in 5 hours and 45 minutes. Since there is 60 minutes every hour, 6 x 5 + 45 = 300 + 45 = 345. 1.1333333333 x 345 = 390.9999999885, rounded = 391.