When iodine crystals are added to chloroform, a chemical reaction takes place, resulting in the formation of iodine trichloride (ICl3). This reaction can be represented as follows:

I2 (s) + 3CHCl3 (l) → ICl3 (l) + 3HCl (g)

In this reaction, the iodine crystals undergo a disproportionation reaction, where one iodine atom is oxidized to form ICl3 while the other iodine atom is reduced to form HCl gas. The reaction is exothermic, releasing heat into the surroundings.

The formation of ICl3 results in a visible change in the solution. Initially, the solution may appear dark brown or reddish-brown due to the presence of iodine crystals. As the reaction progresses and ICl3 is formed, the solution gradually becomes lighter in color and may eventually become colorless or pale yellow.