In chemical kinetics, zeroth order refers to a reaction rate that is:

In chemical kinetics, zeroth order refers to a reaction rate that is:

• A. Independent of reactant concentration
• B. Proportional to the square of concentration
• C. Proportional to the concentration
• D. Proportional to temperature only

Answer: (A)

Zero-order kinetics means the rate is governed by something other than how much reactant is present, so changing the concentration doesn’t change the rate. The rate law is written as rate = k, so the consumption of A is -d[A]/dt = k. That makes the concentration of A fall linearly with time: [A] = [A]0 − kt. Because the rate does not depend on [A], this description best matches a zeroth-order process. The other possibilities correspond to different dependencies: a rate proportional to [A] squared is second order, proportional to [A] is first order, and a statement that the rate is determined by temperature only would ignore the usual concentration dependence (even though k itself changes with temperature via Arrhenius).

Zero-order kinetics means the rate is governed by something other than how much reactant is present, so changing the concentration doesn’t change the rate. The rate law is written as rate = k, so the consumption of A is -d[A]/dt = k. That makes the concentration of A fall linearly with time: [A] = [A]0 − kt. Because the rate does not depend on [A], this description best matches a zeroth-order process.

The other possibilities correspond to different dependencies: a rate proportional to [A] squared is second order, proportional to [A] is first order, and a statement that the rate is determined by temperature only would ignore the usual concentration dependence (even though k itself changes with temperature via Arrhenius).