Final answer:
Evidence of a chemical reaction can be determined by signs such as temperature changes, emission of light, unexpected color changes, gas production, and the formation of a precipitate, along with mass changes adhering to the law of conservation of mass.
Step-by-step explanation:
To identify the evidence of a chemical reaction, you should look for several specific signs. First, note any changes in temperature, which could indicate an exothermic or endothermic reaction. Second, observe for any light that may be emitted, a sign of energy release. Third, look for any unexpected color changes which suggest new substances are being formed. Fourth, the formation of bubbles not from boiling indicates that a gas has been produced. Lastly, the formation of a solid precipitate in a liquid solution is another key indicator of a chemical reaction.
Remember, in chemistry, evidence of a reaction also includes a change in mass. This relates to the law of conservation of mass stated by John Dalton's atomic theory, which implies that the mass of the reactants should be equal to the mass of the products if a chemical reaction has occurred properly, without any 'leftovers'. So, after noting the aforementioned visual clues like color change and gas production, you should also reassess the mass of the substances at the end of the reaction compared to their initial mass.