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  

are there answer choices to this question? this seems like a question where you have options to choose from.

+15-35=-20

going in opposite directions