Answer:
acc. to thermodynamics
consider a hot system in a closed containerise can only allow to exchange energy (radiation,heat energy) with the surrounding but not matter..........
but where as in open system eg. open container it can exchange energy ass well as matter(like vapour molecules).
Simply consider hot tea in open Gopher vapours are consider as matter.
Similarly in isobaric process ie. pressure remains constant throughout the system there is no flow of matter within system.
All though matter and energy are interconvertable just don't get confused with Einsteins theory of relativity.
It depends on on what basis you are studying on. Whether physics or chemistry.