Answer:
That's called a first-order reaction.
Explanation:
In kinematics, the order of a chemical reaction is the sum of the power of concentrations in is rate law.
For example, consider a reaction with the following rate law:
[tex]\text{Rate} = k\cdot [\mathrm{A}]^{a}\cdot [\mathrm{B}]^{b}[/tex],
where [tex][\mathrm{A}][/tex] and [tex][\mathrm{B}][/tex] are the concentrations of the two reactants, [tex]\mathrm{A}[/tex] and [tex]\mathrm{B}[/tex].
The order of this reaction will be equal to the sum of the powers of the concentrations in the rate law. For this sample reaction, the order is equal to [tex]a + b[/tex].
For the reaction in this question, the rate law will resemble the following:
[tex]\text{Rate} = k\cdot [\mathrm{A}][/tex].
Note that the power "[tex]1[/tex]" next to the concentration of [tex]\mathrm{A}[/tex] is omitted. The order of this reaction will be numerically equal to one.
However, by convention, the order of the reaction is named in ordinals. (That is: first, second, third, etc.) The reaction here is known as a first-order reaction.
(Reference: "The Rate Law", Physical & Theoretical Chemistry, Chemistry Libretexts; "Cardinal and Ordinal Numbers Chart", Math Is Fun)
