Question

1. which of the following options best provides observable evidence that a chemical change has taken place? a. a darkening of color and evaporation of the substance b. particles dissolved in the substance c. production of a gas or precipitate or change in thermal energy or color d. change in shape of the original substance

Explanation:

A chemical change results in the formation of a new substance. Production of a gas, formation of a precipitate, and changes in thermal energy or color are common signs of chemical changes. A darkening of color and evaporation (A) are physical changes in many cases. Particles dissolving (B) is a physical change - dissolution. A change in shape (D) is a physical change. But production of a gas or precipitate or change in thermal energy or color (C) indicates a chemical reaction has occurred.

Answer:

C. Production of a gas or precipitate or change in thermal energy or color