A person is going for a walk in the evening. To make sure that she can be seen walking when it gets dark, she wears a glow stick around her neck. The glow stick can be used as a light source when she bends the stick. Although the stick is sealed, bending the stick allows two chemicals to come in contact and react with each other. During the chemical reaction, light is given off by the glow stick. When the reaction stops, light is no longer given off. What happens to the mass of the glow stick after the chemical reaction occurs? Explain citing evidence from the prompt and identify the scientific law that supports your explanation.

(give me claim, evidence, reasoning)