Question

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?

Answer 1

75%

Explanation:

"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.

Answer 2

`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`.