What occurs when bromine water is mixed with an alkene?

When bromine water is mixed with an alkene, a color change occurs because bromine reacts with the alkene through an addition reaction. Alkenes contain carbon-carbon double bonds, which are reactive sites for bromine. When bromine, which is typically a reddish-brown color, interacts with the alkene, the double bond is broken, and bromine atoms add across the former double bond. This reaction effectively removes the reddish-brown color of the bromine, leading to a decolorization of the solution. The original color of the bromine water fades, confirming that a chemical reaction has taken place.

The other answers reflect a misunderstanding of the reaction. There is a distinct color change associated with this reaction, specifically a loss of the reddish-brown color from the bromine water, rather than no color change, a turn to red, or a shift to blue.