What are the products formed when ammonium dichromate is thermally decomposed?
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The thermal decomposition of ammonium dichromate is an example of an internal redox reaction, where the oxidizing agent (\(Cr_2O_7^{2-}\)) and the reducing agent (\(NH_4^+\)) are part of the same ionic compound. Remember the products: N is oxidized to \(N_2\), Cr is reduced to \(Cr_2O_3\), and the rest forms water.
The thermal decomposition of ammonium dichromate, \( (\text{NH}_4)_2\text{Cr}_2\text{O}_7 \), is a well-known and visually dramatic reaction, often called the "volcano" experiment.
It is an intramolecular redox reaction.
In the ammonium ion (\(\text{NH}_4^+\)), the oxidation state of Nitrogen is -3.
In the dichromate ion (\(\text{Cr}_2\text{O}_7^{2-}\)), the oxidation state of Chromium is +6 (since \(2x + 7(-2) = -2 \implies 2x = 12 \implies x=+6\)).
During the decomposition, the nitrogen in the ammonium ion is oxidized, and the chromium in the dichromate ion is reduced.
Nitrogen (\(-3\)) is oxidized to its elemental form, nitrogen gas (\(N_2\)), which has an oxidation state of 0.
Chromium (\(+6\)) is reduced to Chromium(III) oxide (\(\text{Cr}_2\text{O}_3\)), where its oxidation state is +3.
The hydrogen and remaining oxygen atoms combine to form water (\(H_2O\)).
The balanced chemical equation for the reaction is:
\( (\text{NH}_4)_2\text{Cr}_2\text{O}_7(s) \xrightarrow{\Delta} \text{N}_2(g) + \text{Cr}_2\text{O}_3(s) + 4\text{H}_2\text{O}(g) \).
The products are nitrogen gas, solid chromium(III) oxide (a green powder), and water vapor.
