The formula for the half life is simply:
t1/2 = ln 2 / k
where k is the rate constant and can be calculated from
the formula:
rate = k [A]
where [A] is the initial concn = 0.25 M
k = 4.36 × 10-2 M s-1 / 0.25 M = 0.1744 s-1
t1/2 = ln 2 / 0.1744 s-1
t1/2 = 3.97 s
