For the reaction \(\mathrm{A}+\mathrm{B} \rightarrow \mathrm{C}\), explain at least two ways in which the rate law could be zero order in chemical A.

One possible situation in which the rate law is zero-order in A is if the reaction is a one-step reaction, and A is present at a high enough concentration that it saturates the reactive sites. In this scenario, adding more A has no effect on the reaction rate because all available reactive sites are already occupied. As a result, the rate law for the reaction becomes rate = k [B]^n, showing that it is zero-order in A.

Another possibility for the rate law to be zero-order in A is if the reaction is a two-step reaction, in which A is involved only in the second step along with chemical C. In the first step, B reacts with another molecule to form C, and in the second step, A and C react to form the final products. Since the second step is generally faster than the first step, the reaction rate is primarily determined by the first step, not by A. This means that the rate law for this reaction would depend only on the concentration of B and not on A, making the reaction zero-order in A. In both scenarios, the rate of the reaction is independent of the concentration of chemical A, and hence the rate law shows zero-order dependence on A.