To observe a chemical property, a chemical change must occur (new substances produced). To see if a piece of paper has the chemical property of combustability (will burn in oxygen), you must actually try to burn it, producing carbon (ash), water vapor, carbon dioxide – the material is no longer paper. What are some clues, observations that might indicate that a chemical change has occurred?

Explanation:

Chemical reaction is described as the process of rearrangement of the atoms to produce a new product which will have a different chemical identity.

For the observatory evidences to prove a chemical reaction has occurred we can look to the following:

Absolute result for the chemical change can be observed using the chemical analysis  

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.