Question

 A first-order reaction is 50% completed in 1.26 x 10¹⁴ s. How much time would it take for 100% completion?

(a) 1.26 x 10¹⁵ s
(b) 2.52 x 10¹⁴ s
(c) 2.52 x 10²⁸ s
(d) infinite

Answer 1

(d) infinite

The whole of the substance never reacts because in every half-life, 50% of the substance reacts. Hence, the time taken for 100% completion of a reaction is infinite.