The reaction of potassium dichromate (K₂Cr₂O₇) with nitric acid (HNO₃) is a bit nuanced and depends on the concentration of nitric acid. Here's a breakdown:

1. With dilute nitric acid:

* The reaction is primarily an acid-base reaction.

* The dichromate ion (Cr₂O₇²⁻) acts as a weak base and reacts with nitric acid to form chromic acid (H₂CrO₄).

* The reaction can be represented as:

```

K₂Cr₂O₇ + 2 HNO₃ → 2 KNO₃ + H₂CrO₄

```

* The chromic acid is unstable and readily decomposes into water and chromium trioxide (CrO₃):

```

H₂CrO₄ → H₂O + CrO₃

```

* The overall reaction can be written as:

```

K₂Cr₂O₇ + 2 HNO₃ → 2 KNO₃ + H₂O + CrO₃

```

2. With concentrated nitric acid:

* In this case, the reaction is more complex and involves oxidation.

* Concentrated nitric acid acts as a strong oxidizer, oxidizing the dichromate ion.

* The reaction produces chromium trioxide (CrO₃), nitrogen dioxide (NO₂), and water.

```

K₂Cr₂O₇ + 4 HNO₃ → 2 KNO₃ + 2 CrO₃ + 2 NO₂ + 2 H₂O

```

Important Notes:

* The reaction with concentrated nitric acid is highly exothermic and can be dangerous.

* Potassium dichromate and chromium compounds are toxic and carcinogenic. Handle them with caution and always wear appropriate safety gear.

* The reaction is also sensitive to temperature and concentration.

Let me know if you have any other questions.