Question

1. when observed independently, which of the following are indications that a chemical reaction has occurred? select all that apply. temperature change formation of a precipitate melting of a solid change in odor evaporation of a liquid

Explanation:

• Temperature change: Chemical reactions can release or absorb heat (exothermic/endothermic), causing a temperature change. This is an indication of a chemical reaction.
• Formation of a precipitate: When two solutions react to form an insoluble solid (precipitate), it shows a chemical reaction has occurred (e.g., double - displacement reactions).
• Melting of a solid: This is a physical change (phase change from solid to liquid) and does not involve a chemical reaction.
• Change in odor: A new substance with a different odor being formed (due to chemical bonds breaking and forming) indicates a chemical reaction.
• Evaporation of a liquid: This is a physical change (phase change from liquid to gas) and not a chemical reaction.

Answer:

• Temperature change
• Formation of a precipitate
• Change in odor