Final answer:
Signs of a chemical reaction include changes in temperature, formation of a gas, a change in color, and the appearance of a solid precipitate.
Step-by-step explanation:
When conducting a lab to observe a chemical reaction , there are several signs that can indicate a reaction has occurred. These include a changes in temperature , which could be a temperature increase or decrease, signifying an exothermic or endothermic reaction. Another indication is the formation of a gas, often evidenced by bubbles that are not due to boiling. A change in color can also suggest a chemical reaction, particularly if a new color emerges that is different from the colors of the starting materials. Finally, the formation of a solid, known as a precipitate., indicates a chemical change, especially if the solid forms in a liquid where none existed before. These changes are crucial observations that help scientists and students confirm the occurrence of a chemical reaction.