Question

A first order reaction takes 80 min for 50% completion. What fractionof a givn sample will remain after 2 hours

Answer 1

80 min for 50%

1 min for 50/80 %

2 hours = 120 min for 120*50/80 = 75%

ie, 75% completes

and 100 - 75 = 25% will remain after two hours