Which term describes a change that creates a new substance and is irreversible?

The term that describes a change that creates a new substance and is irreversible is a chemical change. In a chemical change, the molecular structure of the substance is altered, resulting in the formation of one or more new substances that have distinct properties from the original material. This process involves breaking of chemical bonds and forming new ones, which cannot be undone easily, if at all, under normal conditions.

For example, when iron rusts, it undergoes a chemical change as it reacts with oxygen and moisture to form iron oxide, a new substance that cannot revert back to iron through physical means. Understanding chemical changes is crucial in various fields, including mortuary science, as certain reactions occur during embalming and decomposition that are critical to the preservation and processing of human remains.

In contrast, physical changes do not result in the formation of new substances and can often be reversed, such as melting ice into water. Phase changes involve transitions between states of matter (solid, liquid, gas) without changing the chemical identity of the substance. Geological change typically refers to large-scale changes in the earth's structure or composition over time, which do not directly relate to chemical processes at the molecular level.