For a first-order reaction, the time required for x % completion is exactly twice the time required for 90 % completion. The value of x is:

Step-by-step solution

For a first-order reaction, the time t required for a certain percentage completion is given by the integrated rate law: t = 1 k ( 100 100 - percentage ) The time required for 90 % completion is: t_ 90 % = 1 k ( 100 100 - 90 ) = 1 k (10) The time required for x % completion is given as twice t_ 90 % : t_ x % = 2 t_ 90 % = 2 k (10) = 1 k (10^2) = 1 k (100) Equating this to the standard formula for x % completion: 1 k ( 100 100 - x ) = 1 k (100) 100 100 - x = 100 100 - x = 1 x = 99 Answer: 99