ou snap a glowstick open and it begins to glow a bright yellow color and feels warm in your hand. physical or chemical

The reaction that occurs when you snap a glowstick open is a chemical reaction. Inside the glowstick, there are two separate substances that, when mixed together, undergo a chemiluminescent reaction, producing light. The warmth you feel in your hand is a result of the energy released during this exothermic reaction. Therefore, this process is primarily a chemical change.