What type of evidence would suggest a chemical change has taken place?

A change in color is a strong indicator that a chemical change has occurred. This transformation often signifies that new substances are being formed as a result of a chemical reaction. For instance, when iron rusts, it changes from a shiny metallic color to a reddish-brown color due to the formation of iron oxide. This color change can occur alongside other indicators of a chemical reaction, such as the production of gas or a change in temperature, but the key aspect of color change is that it is often accompanied by changes in the composition of the substance, confirming that a new chemical entity has been created.

Changes in mass or texture may not directly indicate a chemical reaction has taken place; mass changes can result from physical processes, and textures can change due to various non-chemical alterations. A change in temperature can suggest a chemical reaction, especially if it's associated with an exothermic or endothermic process, but it alone does not confirm a new substance has been formed without accompanying evidence, such as a color change.