Multiple Choice
Given the reaction A + 2B → C + 2D, which of the following is an incorrect statement about the rate of the reaction?
15. Chemical Kinetics
Rate Law
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For the reaction A + B → C + D, the reaction rate decreases from 1.80 M/s to 0.20 M/s when [A] decreases from 3 M to 1 M; the reaction rate does not change when [B] increases from 1 M to 2 M. Which of the following is the correct rate law for the reaction?
A
Rate = k[A]^2
B
Rate = k[A]
C
Rate = k[B]^2
D
Rate = k[A][B]
Verified step by step guidance1
Step 1: Understand the concept of rate law. The rate law expresses the rate of a chemical reaction as a function of the concentration of its reactants. It is generally written as Rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to reactants A and B.
Step 2: Analyze the given data. The reaction rate decreases significantly when [A] decreases from 3 M to 1 M, indicating that the rate is dependent on the concentration of A. However, the rate does not change when [B] increases from 1 M to 2 M, suggesting that the rate is independent of the concentration of B.
Step 3: Determine the order of the reaction with respect to A. Since the rate decreases as [A] decreases, A must be part of the rate law. The significant change in rate suggests a higher order with respect to A, likely second order, as the rate decreases from 1.80 M/s to 0.20 M/s.
Step 4: Determine the order of the reaction with respect to B. Since the rate does not change when [B] is increased, B is not part of the rate law, or its order is zero. This means the rate is independent of [B].
Step 5: Formulate the rate law based on the analysis. Given that the rate is dependent on [A] and independent of [B], the correct rate law is Rate = k[A]^2, indicating a second-order reaction with respect to A and zero-order with respect to B.
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