Zero order describes?

Zero order describes?

• A. Rate equals k.
• B. Rate is directly proportional to [A].
• C. Changing the concentration of the reactant has no effect on the rate.
• D. Rate is proportional to the square of [A].

Answer: (C)

Zero order means the reaction rate does not change when the concentration of the reactant is varied. In this case the rate law is rate = k, so the speed of the reaction is constant and set by the mechanism rather than by how much A is present. This happens when the step that controls the rate is saturated—like a catalyst surface or a limited reactive site—so adding more reactant doesn’t speed things up. Saying the rate equals k conveys this constant-rate idea in simple terms, but the key point to grasp is the lack of dependence on [A]. If changing [A] changed the rate, that would reflect a different order (first order or second order, etc.).

Zero order means the reaction rate does not change when the concentration of the reactant is varied. In this case the rate law is rate = k, so the speed of the reaction is constant and set by the mechanism rather than by how much A is present. This happens when the step that controls the rate is saturated—like a catalyst surface or a limited reactive site—so adding more reactant doesn’t speed things up. Saying the rate equals k conveys this constant-rate idea in simple terms, but the key point to grasp is the lack of dependence on [A]. If changing [A] changed the rate, that would reflect a different order (first order or second order, etc.).