PSI Barbering Practice Exam

Which statement is true about chemical changes?

1. They are often reversible.

2. They form new substances.

3. They only involve physical properties.

4. They do not involve energy changes.

The correct answer is: They form new substances.

Chemical changes are characterized by the transformation of substances into new substances through the breaking and forming of chemical bonds. This process results in alterations to the chemical structure and properties of the original materials, leading to the creation of different substances with distinct characteristics. For example, when iron rusts, it undergoes a chemical change that results in the formation of iron oxide, which differs from elemental iron. In contrast, the other options do not accurately reflect the nature of chemical changes. While some chemical reactions can be reversible, many are not, making the idea of reversibility a less reliable characteristic. The involvement of physical properties is further associated with physical changes, not chemical ones. Additionally, energy changes, such as heat release or absorption, are generally a significant part of chemical reactions, as they often occur alongside the chemical changes. Understanding these aspects reinforces why the formation of new substances is the defining feature of chemical changes.