When heated, ammonium dichromate undergoes decomposition into various products. The primary decomposition reaction is:

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

In this reaction, ammonium dichromate breaks down to form chromium(III) oxide (Cr2O3), nitrogen gas (N2), and water vapor (H2O).

2. Color Changes:

As ammonium dichromate decomposes, it undergoes distinct color changes. Initially, the compound is orange or reddish-orange in color. As heating progresses, it transforms through various shades of red, brown, and finally to a dark green residue of chromium(III) oxide.

3. Evolution of Gases:

During decomposition, ammonium dichromate releases gases. Nitrogen gas (N2) is produced as a result of the breakdown of the ammonium group. Additionally, water vapor (H2O) is formed due to the presence of water molecules in the compound.

4. Exothermic Reaction:

The decomposition of ammonium dichromate is an exothermic reaction, meaning it releases heat. This heat release can cause a self-sustaining reaction, resulting in rapid decomposition and the evolution of large amounts of gases.

5. Catalyst for Organic Reactions:

Ammonium dichromate acts as a catalyst in various organic reactions. It is commonly used in the oxidation of alcohols to aldehydes or ketones. For instance, it converts primary alcohols into aldehydes and secondary alcohols into ketones.

Overall, the decomposition of ammonium dichromate involves color changes, gas evolution, heat release, and its use as a catalyst in organic reactions.