A glow stick is not a gas-liquid solution, it is a chemiluminescent device. Chemiluminescence is the emission of light as a result of a chemical reaction. In a glow stick, the chemical reaction that produces light is between hydrogen peroxide and a fluorescent dye. The hydrogen peroxide is stored in a glass vial and the fluorescent dye is in a plastic tube. When the glass vial is broken, the hydrogen peroxide and the fluorescent dye mix and react, producing light.