Question

what are the main indications that a chemical reaction has occurred?
check all that apply.

□ emission of light
□ a color change
□ change of the state of matter
□ emission of (or absorption of) heat
□ formation of a solid
□ formation of a gas

Explanation:

To determine the indications of a chemical reaction, we analyze each option:

• Emission of light: Some reactions (like combustion or chemiluminescence) emit light, indicating a chemical change.
• A color change: A change in color often signals the formation of new substances (e.g., rusting, indicator reactions).
• Change of the state of matter: Phase changes (like melting) are physical, not chemical, so this is incorrect.
• Emission/absorption of heat: Exothermic (heat release) or endothermic (heat absorption) reactions show chemical change (e.g., burning, dissolving ammonium nitrate).
• Formation of a solid: Precipitation (e.g., mixing solutions to form a solid) is a chemical reaction indicator.
• Formation of a gas: Gas production (e.g., baking soda + vinegar) indicates a chemical reaction.

Answer:

A. emission of light, B. a color change, D. emission of (or absorption of) heat, E. formation of a solid, F. formation of a gas