Answer:
It would take 20 seconds
Explanation:
Let the final concentration of AB be C
Rate = k[C]^2 = change in concentration of AB/time
k is the rate constant = 0.2 L/mol.s
Initial concentration of AB = 1.5 M
Final concentration of AB = 1/3 × 1.5 = 0.5 M
Change in concentration of AB = 1.5 - 0.5 = 1 M
0.2 × 0.5^2 = 1/time
time = 1/0.05 = 20 s