AFOQT Practice Test 2025 - Free AFOQT Questions and Complete Study Guide

A chemical change is defined as a process in which one or more substances undergo a transformation to become entirely new substances. This transformation involves breaking and forming bonds between atoms, resulting in different chemical properties and structures than the original substances. For instance, when iron rusts, it reacts with oxygen to form iron oxide, which is a completely different material compared to the original iron and oxygen. This change is usually not reversible by simple physical means, further indicating the formation of new substances.

In contrast, physical changes, mechanical changes, and thermal changes do not result in the creation of new substances; they involve alterations in the form or state of a substance without changing its chemical identity.