Describe the industrial preparation of nitric (V) acid using the Ostwald process, including the chemical equations for each step.

Ammonia ($\text{NH}_3$) and air (source of $\text{O}_2$) are mixed and passed over a heated **platinum-rhodium catalyst** at about $800-900^\circ\text{C}$ and $4-10$ atmospheres pressure. This produces nitric oxide ($\text{NO}$) and water.
$$
4\text{NH}_3\text{(g)} + 5\text{O}_2\text{(g)} \xrightarrow{\text{Pt/Rh catalyst}} 4\text{NO(g)} + 6\text{H}_2\text{O(g)}
$$

The hot nitric oxide is cooled and then reacted with excess air (oxygen) in an oxidation chamber. This converts nitric oxide to nitrogen dioxide ($\text{NO}_2$).
$$
2\text{NO(g)} + \text{O}_2\text{(g)} \rightarrow 2\text{NO}_2\text{(g)}
$$

The nitrogen dioxide is then passed into an absorption tower where it reacts with water, usually sprayed from the top. This forms nitric (V) acid ($\text{HNO}_3$) and regenerates nitric oxide ($\text{NO}$).
$$
3\text{NO}_2\text{(g)} + \text{H}_2\text{O(l)} \rightarrow 2\text{HNO}_3\text{(aq)} + \text{NO(g)}
$$

The nitric oxide ($\text{NO}$) produced in the absorption tower is recycled back to the oxidation chamber (Step 2) to be re-oxidized to nitrogen dioxide, making the process more efficient.