A 15 gram substance that's has a k value of 0.1405. what's the half life

Answer 1

A(t) = A_oe^kt

Since it's the half-life we are interested in, we know that A(t) will be half the original amount, A_o:

A_o/2 = A_oe^-kt

1/2 = e^-kt

ln(1/2) = -kt_1/2

t_1/2 = -ln(1/2)/k

t_1/2 = -ln(1/2)/0.1405

t_1/2 = 4.93

*Note: I left my answer unitless since you didn't provide any units for time*