Which process involves breaking and reforming chemical bonds to create a new substance?

The process that involves breaking and reforming chemical bonds to create a new substance is a chemical reaction. During a chemical reaction, the atoms in the reactants rearrange themselves to form products, resulting in the formation of new chemical substances with different properties from the original ones. This transformation is characterized by the creation or destruction of chemical bonds, which is the hallmark of a chemical change.

In contrast, a physical change involves alterations in physical properties such as shape, state, or appearance, but does not change the chemical composition of the substance. Phase changes, such as melting or boiling, are specific types of physical changes that only involve a change in the state of matter without any alteration in the chemical bonds. Mechanical reactions do not refer to any recognized process in chemistry related to the transformation of substances on a molecular level. Thus, chemical reactions are distinct because they lead to the formation of new substances through the breaking and making of bonds.