What is the observation when an alkane reacts with bromine water in UV light?

When an alkane reacts with bromine water in the presence of UV light, the observation is that the orange color of the bromine disappears slowly. This reaction is a type of free radical substitution reaction, where the bromine molecules are broken apart by the energy provided by UV light, generating bromine radicals. These radicals then react with the alkane, leading to the substitution of hydrogen atoms with bromine atoms.

As the reaction progresses, the bromine, which is typically orange in color, is consumed, resulting in a decrease in color intensity. The reaction is relatively slow compared to reactions involving alkenes, where bromine adds across the double bond rapidly, leading to an immediate decolorization. The disappearance of the orange color indicates that bromination is taking place and provides clear evidence of the reactivity of the alkane under these conditions.