A certain reaction follows zero-order kinetics. Suppose the reaction went to #50%# completion after #10# minutes. What percentage of completion does the reaction reach in an additional #5# minutes?

"Zero order" kinetics means that the rate = k and is independent of the amount of material present. Thus, if the rate is such that the reaction is 50% complete in 10 minutes, in another 5 minutes another 25% of the overall reaction is complete - 75% of the total reaction.

The total reaction will be completed in 20 minutes.

#75%# complete.

A reaction following zero order kinetics has the rate law:

#r(t) = k[A]^0[B]^0 cdots#

and the rate is equal to the rate constant. Consequently, the rate of consumption of all the reactant(s) is a constant, and one could plot concentration #[A]# of reactant #A# vs. time #t# to model the reaction progress.

This curve would then be a straight line:

And as such, it allows us to use the reaction progress as indicative of the fraction of #[A]# leftover. #50%# completion therefore means #50%# of #[A]# is gone.

Since that occurred in #10# minutes, and the rate is constant, in #5# minutes the reaction proceeds by half of #50%#. As a result, the reaction is #color(blue)(ul(75%))# complete after #5# additional minutes, or #[A] = 0.25[A]_0#.