1. For a reaction mechanism to be plausible, what 2 criteria must be met?
2. The reaction between CO and NO2 to produce NO and CO2 is thought to occur in 2 steps.
NO2 + NO2 ====> NO + NO3
NO3 + CO =====> NO2 + CO2
The experimental rate law is, R=k[NO2]2
Write the equation for the overall reaction.
Identify the reaction intermediates.
Identify the rate determining step.
1. To determine if a reaction mechanism is plausible, two criteria must be met:
a) The overall reaction must be consistent with the observed stoichiometry of the reaction. This means that the sum of the elementary steps in the mechanism should lead to the balanced chemical equation for the reaction.
b) The sequence of elementary steps in the mechanism must be consistent with the rate law expression. This means that the slowest (rate-determining) step should have a rate law that matches the experimental rate law for the overall reaction.
2. The given reaction between CO and NO2 occurs in two steps. Let's break it down:
Step 1: NO2 + NO2 → NO + NO3
Step 2: NO3 + CO → NO2 + CO2
To write the overall reaction, we can cancel out the common species (NO2) between the two steps:
2NO2 + CO → NO + NO3 + CO2
The reaction intermediates are the species that appear in the mechanism but not in the overall reaction. In this case, NO3 is the reaction intermediate because it is produced in step 1 and consumed in step 2.
To identify the rate-determining step, we need to compare the kinetics of the elementary steps with the experimental rate law. The given experimental rate law is R = k[NO2]^2.
Looking at the given mechanism, we can see that the rate-determining step is the slowest step, which is step 1 (NO2 + NO2 → NO + NO3). This is because the rate law for the overall reaction is determined by the slowest step in the mechanism. Therefore, in this case, the rate-determining step is step 1.