Final answer:
When observing a chemical reaction after a solid is added to a liquid, key indicators include changes in temperature, light produced, color changes, and bubble formation, all of which signify a chemical change as opposed to physical changes like dissolution or phase changes which do not alter the chemical composition.
Step-by-step explanation:
If a student adds a solid substance to a liquid and a chemical reaction is occurring, they should observe certain signs and changes that indicate a chemical change. Notable observations include temperature changes (either an increase or decrease in temperature), light emission, unexpected color changes, or the formation of bubbles when the substance is not boiling, signifying that a gas at room temperature is being produced. It is important to note that a chemical reaction may not necessarily be accompanied by smoke, as suggested by one of the initial statements, and that the temperature of the solid may indeed change as an indication of a reaction. Moreover, in a chemical reaction, the mass of the reactive systems remains the same before and after the reaction due to the Conservation of Mass, contradicting the idea that the mass of the solid stays the same as a definitive sign of a chemical reaction.