chemical vs chemical substance

chemical and chemical substance both are nouns.

Word	Noun	Adjective	Verb	Adverb
chemical	Yes	Yes	No	No
chemical substance	Yes	No	No	No

As nouns, chemical and chemical substance are synonyms defined as:

chemical and chemical substance: material produced by or used in a reaction involving changes in atoms or molecules

chemical (noun)	chemical substance (noun)
material produced by or used in a reaction involving changes in atoms or molecules	material produced by or used in a reaction involving changes in atoms or molecules

chemical (adjective)	chemical substance (adjective)
relating to or used in chemistry
of or made from or using substances produced by or used in reactions involving atomic or molecular changes