Answer:
t = 20.74 sec
Explanation:
Using integrated rate law for first order kinetics as:
[tex][A_t] =[A_0] -kt[/tex]
Where,
[tex][A_t][/tex] is the concentration at time t = 0.220 M
[tex][A_0][/tex] is the initial concentration = 0.780 M
k is the rate constant = 0.0270 M s⁻¹
So,
[tex]0.220 =0.780 -0.0270\times t[/tex]
t = 20.74 sec