The equation 4HNO3 + CoS -> 2NO2 + 2H2O + Co(NO3)2 + 2S

The chemical equation above describes the reaction process between nitric acid (HNO₃) and cobalt sulfide (CoS). In this process, nitric acid reacts with cobalt sulfide to produce nitrogen dioxide (NO₂), water (H₂O), cobalt nitrate (Co(NO₃)₂) and sulfur (S).

This reaction typically occurs at standard temperature and pressure. However, the reaction rate can be accelerated by increasing the temperature or using an appropriate catalyst.

Reaction process:

• First, nitric acid reacts with cobalt sulfide to form nitrogen dioxide, water, and cobalt nitrate.
• Next, cobalt nitrate continues to react with the remaining nitric acid to produce more nitrogen dioxide and water.
• Finally, sulfur is released into the environment.

Occurring phenomena:

• As the reaction process takes place, the surrounding environment will appear brown due to the formation of nitrogen dioxide.
• The unpleasant smell of nitrogen dioxide can also be perceived.
• In addition, the formation of pink crystalline cobalt nitrate and yellow sulfur powder can be observed.