Entropy of Surroundings vs Entropy of Systems

[805329408]

For reversible reactions, the delta s system is always equivalent to negative delta s surroundings which is equal to delta s system. However, for irreversible reactions, is delta s surroundings always equal to 0? Why? Thanks in advance!

[jisulee1C]

In a reversible reaction there is a change of entropy and because it is isothermal delta U will be zero. However, in an irreversible reaction there is no work done because only free expansion occurs. Therefore since w = 0 and delta U = 0 the q = 0 so the q of surroundings =0 and delta S of the surroundings = 0. There's a section in the textbook that explains this concept more into detail (4I.2 example 4I.3).