What does pure substance mean

A chemical substance is a particular class of homogeneous matter whose composition is fixed and chemically defined and is made up of the following entities: molecules, form units, and atoms.

something that contains only one kind of matter

Explanation:

> b takes place in the gas phase in an isothermal tubular reactor. the feed is one mole of a per one mole of c, an inert. the entering temperature and pressure are 427°c and 10 atm, respectively. the gas constant r = 0.08206 atm · l/mol · k.