NH3 is a reducing agent, CrO3 is an oxidizing agent.
This is a precipitation reaction: Cr2O3 is the formed precipitate.
This is a gas evolution reaction, N2 is the formed gas.
CrO3 – Chromium trioxide
Other names: Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer)
Appearance: Dark red granular solid, deliquescent ; Odourless dark red deliquescent crystals, flakes or granular powder
Names: Ammonia, Azane (only intended for use in naming derivatives of ammonia), Hydrogen nitride
Appearance: Colourless gas ; Colourless gas or compressed liquefied gas with pungent odour ; Colorless gas with a pungent, suffocating odor. [Note: Shipped as a liquefied compressed gas. Easily liquefied under pressure.]