Complex sentence: Many physical changes also involve the rearrangement of atoms most noticeably in the formation of crystals.Chemical changes are irreversible, and physical changes are reversible, but reversibility is not a certain criterion for classification.
Split into simpler sentences: Many physical changes also involve the rearrangement of atoms most noticeably in the formation of crystals. Many chemical changes are irreversible, and many physical changes are reversible, but reversibility is not a certain criterion for classification.