is not a glow stick open and it begins to glow a bright yellow color and feels warm in your hand. Is that physical or chemical change?

The glowing of a glow stick when it is opened is a chemical change. This occurs because the substances inside the glow stick undergo a chemical reaction when exposed to air (or when the stick is cracked to mix the chemicals), producing light and heat. The glow is due to a process called chemiluminescence, which involves a chemical reaction that emits light. Therefore, the glow stick’s transformation is a chemical change rather than a physical one.