Multiple Choice
A plot of ln[A] versus time yields a straight line with slope -0.0045/s. What is the value of the rate constant (k) for this reaction at this temperature, and what is the rate law for the reaction?
15. Chemical Kinetics
Rate Law
Multiple Choice
Consider a multistep reaction where the slowest (rate-determining) step is: 2 NO_2(g) → NO_3(g) + NO(g). What is the best rate law for the overall reaction?
A
rate = k[NO_3]^2
B
rate = k[NO_2]^2
C
rate = k[NO_2][NO_3]
D
rate = k[NO_2]
Verified step by step guidance1
Identify the rate-determining step (RDS) in the reaction, which is the slowest step controlling the overall reaction rate. Here, the RDS is given as: 2 NO_2(g) → NO_3(g) + NO(g).
Write the rate law expression based on the molecularity of the rate-determining step. Since the RDS involves two NO_2 molecules reacting, the rate law depends on the concentration of NO_2.
Express the rate law as: \(\text{rate} = k[\mathrm{NO}_2]^2\), where \(k\) is the rate constant and the exponent 2 corresponds to the stoichiometric coefficient of NO_2 in the RDS.
Understand that intermediates like NO_3 and products like NO do not appear in the rate law unless they are involved in the rate-determining step or affect the rate directly.
Conclude that the best rate law for the overall reaction is \(\text{rate} = k[\mathrm{NO}_2]^2\), reflecting the dependence on the reactant concentration in the slowest step.
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