The concentration of H₂O in the stratosphere is about 5 ppm. It undergoes photodissociation according to: H₂O(g) → H(g) + OH(g)
(c) The hydroxyl radical, OH, can react with ozone, giving the following reactions:
OH(g) + O₃(g) → HO₂(g) + O₂(g)
HO₂(g) + O(g) → OH(g) + O₂(g)
What overall reaction results from these two elementary reactions? What is the catalyst in the overall reaction? Explain.

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Identify the two given elementary reactions: 1) OH(g) + O3(g) → HO2(g) + O2(g) and 2) HO2(g) + O(g) → OH(g) + O2(g).

To find the overall reaction, add the two elementary reactions together. This involves adding the reactants and products of both reactions.

Cancel out any species that appear on both sides of the resulting equation. In this case, OH(g) appears as both a reactant and a product, so it can be canceled out.

After canceling out the common species, write down the remaining reactants and products to form the overall reaction.

Identify the catalyst in the reaction. A catalyst is a substance that is present at the start and end of the reaction without being consumed. In this case, OH(g) is the catalyst as it is regenerated in the process.

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