Michigan Esthetician State Board Practice Exam

Which of the following best describes the process when iron rusts and wood burns?

1. Physical properties

2. Mechanical changes

3. Chemical properties

4. Thermal properties

The correct answer is: Chemical properties

The correct choice illustrates a fundamental principle of chemistry related to the transformation of substances. When iron rusts, it undergoes a reaction with oxygen and moisture, resulting in iron oxide, commonly known as rust. This process is a chemical change because it involves the formation of new chemical substances with different properties than the original iron. Similarly, when wood burns, it reacts with oxygen in a combustion process, producing ash, carbon dioxide, and water vapor. This transformation also represents a chemical change, as the original substances (wood and oxygen) are converted into entirely new products that cannot revert back to their original forms through simple physical means. In both scenarios, the alterations in the fundamental composition of the substances involved are what characterize them as chemical changes rather than physical properties, which primarily concern observable characteristics like color or state without changing the chemical identity. Mechanical changes pertain to changes related to the physical form or structure without altering the composition, which is not the case here. Thermal properties relate to the behavior of materials in response to heat, which is not the main focus of rusting or burning processes.