Can entropy change be positive for both a system and its surrounding?
1 Answer
If the system is defined in a certain way, then yes.
Suppose you had a combustion of propane.
#"C"_3"H"_8(l) + 5"O"_2(g) -> 3"CO"_2(g) + 4"H"_2"O"(g)#
If you define the system as the chemical bonds, but the surroundings as the reaction vessel (and outside it), then the system loses entropy (since heat is released in the overall reaction) but the surroundings gain entropy (since heat is dispersed into the surroundings from the system, and more gases are also formed).
If you define the system as the reaction or reaction vessel and the surroundings as outside a reaction vessel closed to mass transfer but open to heat transfer, then the system gains entropy (due to increased mols of gas creating more motion) and the surroundings also gain entropy (due to released, dispersed heat).
