Question

In your reading, perhaps you saw that in 1995, three chemists were awarded the Nobel Prize for their studies involving the ozone layer. First, in 1970, scientist Paul Cruzen hypothesized that nitrogen oxides could participate in the destruction of ozone. He was concerned that high-flying jet aircrafts, such as the Concorde, could be the culprit that created the nitrogen oxide. He proposed the following mechanism to show how these compounds were involved in the destruction of ozone:

Step 1: NO(g) + O3(g) → NO2(g) + O2(g)
Step 2: NO2(g) + O(g) → NO(g) + O2(g)
The rate equation for this reaction was found to be:
Rate of reaction = k[NO][O3]

Looking at this rate law, which of the above steps would be the rate determining step and why?

Answer 1

The rate determining step in this reaction is step 1, in which NO reacts with O3 to form NO2 and O2.

Step-by-step explanation:

The rate determining step in a reaction is the slowest step in the overall reaction mechanism. In this case, we have two steps:

1. NO(g) + O3(g) → NO2(g) + O2(g)
2. NO2(g) + O(g) → NO(g) + O2(g)

To determine which step is the rate determining step, we need to compare the reactants and products in each step. In step 1, we can see that the reactants are NO and O3, while the products are NO2 and O2. In step 2, the reactants are NO2 and O, and the products are NO and O2.

Based on the rate equation, Rate of reaction = k[NO][O3], we can see that the rate of the reaction is dependent on the concentrations of both NO and O3. Therefore, the rate determining step must be the step that involves the formation of NO2, as it is the only step that includes NO, which is a reactant in the rate equation. Thus, the rate determining step is step 1, in which NO reacts with O3 to form NO2 and O2.