What are some signs to look for when determining if a chemical reaction has taken place?

There are a few telltale signs that can help indicate that a chemical reaction has taken place; these include the creation of one or more new substances and a noticeable energy change from the reaction site. However, telling whether a chemical reaction has actually taken place is not always very easy to observe.

These changes can be noted in two different ways, through appearance changes and energy changes.

Appearance changes:

• Gas is released
• A solid appears or disappears
• There is a color change

Energy changes:

• The temperature changes
• Light or flames are seen
• Sound is heard

It is important to note that these signs are merely indicators, not proof, that a reaction has taken place and that the only true sign that a chemical reaction has occurred is the creation of one or more substances as a result of the chemical interaction.