When ammonium dichromate ((NH₄)₂Cr₂O₇) is strongly heated, it undergoes a dramatic and exothermic decomposition reaction, producing a spectacular display of green "volcano" due to the formation of chromium(III) oxide (Cr₂O₃).

Here's what happens:

Reaction:

(NH₄)₂Cr₂O₇(s) → Cr₂O₃(s) + N₂(g) + 4H₂O(g)

Explanation:

* Decomposition: Ammonium dichromate breaks down into simpler substances.

* Exothermic: The reaction releases a significant amount of heat, causing the mixture to become red hot.

* Green "volcano": The heat causes the solid ammonium dichromate to melt and then decompose rapidly, producing a large volume of nitrogen gas (N₂) and water vapor (H₂O). The reaction also produces chromium(III) oxide (Cr₂O₃), a green solid, which is expelled from the reaction mixture. The escaping gases push the green solid upwards, creating the volcano-like effect.

Safety Precautions:

Ammonium dichromate is a strong oxidizing agent and can be toxic. The reaction should be performed in a well-ventilated area, and safety goggles and gloves should be worn. It is also important to avoid inhaling the fumes produced by the reaction.

In summary: Heating ammonium dichromate leads to a dramatic decomposition reaction that produces a green solid (Cr₂O₃), nitrogen gas, and water vapor, creating a striking visual effect.