What evidence indicates that matter changed during the burning of ethanol?

The burning of ethanol is a chemical reaction known as combustion, which involves the transformation of substances and the release of energy. In this process, the evidence that most clearly indicates a change in matter is the formation of ash. This occurs because the combustion of ethanol results in the production of new substances—carbon dioxide and water—along with solid residues, which can manifest as ash.

When a substance burns, it undergoes a chemical transformation where the original molecules of ethanol react with oxygen, breaking apart and reconfiguring into entirely different molecules. Ash, as a product of incomplete combustion, signifies that not all the ethanol is converted into gas, and instead, some solid materials are left behind. This formation of new substances demonstrates that matter has changed during the combustion process.

In contrast, other options may indicate physical processes or changes that do not necessarily confirm a transformation of matter. For instance, an increase in temperature might signify an exothermic reaction but doesn't indicate what substances were present before and after. Color changes in bromothymol blue suggest changes in acidity but don't directly show matter changing. The release of gas is also an important byproduct of combustion, indicating that gas has been formed, but it does not illustrate the specific changes in matter like ash