# 36.2: Introduction


When two substances chemically react, a new substance is formed.  The new substance may have a different color or temperature than the original substances, or may be in a different phase.  There are several indicators that a chemical change has occurred, and multiple indicators may occur in a single reaction.  If no added energy is required to start the reaction, then it is a spontaneous reaction, even if the reaction takes a while to progress.  Stirring is not typically regarded as adding energy.  A spontaneous chemical reaction does not mean the reaction happens quickly, but rather that the atoms will naturally react when placed into contact.

Warnings

• Bleach and hydrogen peroxide can irritate eyes and skin
• Bleach and food coloring can stain clothing
• Notify your instructor of any spills and/or glass breakage
• It is important to wash glassware, including thermometers, between uses

## Contributors and Attributions

36.2: Introduction is shared under a CC BY license and was authored, remixed, and/or curated by LibreTexts.