Doubt from second law of thermodynamics

[vijayramakrishnan]

q_rev/T = ΔS

here what does ΔS signify?does it mean change in entropy of system or surroundings?

how is entropy of system,surrounding and universe related to each other and which entropy is used in gibbs free energy equation?

 

[DrDu]

Delta S is usually the entropy of the system, if not otherwise stated. Specifically, in the Gibbs equation it is the entropy of the system. Personally, I don't think it is appropriate to speak of the entropy of the universe as a whole.