A student observes several reactions. Describe one observation the student might make that would indicate a chemical reaction has taken place.

A student might observe a change in color. For example, if two clear solutions are mixed together and the resulting solution is a different color, this is a strong indication that a chemical reaction has occurred.

Another observation could be the formation of a precipitate. A precipitate is a solid that forms and settles out of a liquid mixture. If a student mixes two solutions together and sees a solid form, this is a sign of a chemical reaction.

The student might also observe a gas being produced. This could be seen as bubbles forming in the solution or even a noticeable smell.

Changes in temperature or light can also indicate a chemical reaction. If the mixture becomes hot or cold, or if light is produced or absorbed, these are signs of a chemical reaction.

Finally, the student might observe a change in properties. For example, if a brittle substance becomes malleable, or a colorless gas turns into a colored gas, these are signs of a chemical reaction.