Pennsylvania Esthetician State Board Practice Exam

What defines a chemical change?

1. A change in physical appearance

2. A process that creates a new substance with different characteristics

3. A reversible reaction

4. A mere temperature change

The correct answer is: A process that creates a new substance with different characteristics

A chemical change is characterized by a process that creates a new substance with different characteristics from the original materials involved in the reaction. This often includes changes in observable properties such as color, odor, and taste, as well as changes at the molecular level where bonds are broken or formed. For instance, when iron rusts, it combines with oxygen to form iron oxide, which has properties distinct from those of elemental iron and oxygen. This transformation illustrates how a chemical change results in the formation of a substance that is fundamentally different from the starting materials. The other options do not capture the essence of a chemical change. A change in physical appearance might occur during a physical change and does not necessarily indicate a change in chemical composition. A reversible reaction can refer to some chemical changes, but many chemical changes are not reversible. Lastly, a mere temperature change usually pertains to physical changes or the energy involved in physical processes, rather than indicating the creation of a new substance.