Hi! I have trouble with the following: 1) Consider an ericsson cycle. It is easy to calculate the change of entropy of the working substance during the isothermal parts. But assuming that all the heat transferred/removed from the working substance during the isobaric processes is done by direct thermal contact with reservoirs at constant temperatures A and B, does this imply the change of entropy of the working substances to be 0? 2) If we don't make the above assumption, adding all the processes of the ericsson cycle together give a net change of entropy to be 0. Why does the change of entropy of a working substance taken around a closed cycle (even including irreversible processes) is always equal to 0? 3) A corrolary question: When calculating the change of entropy of the universe when the ericsson engine goes around one cycle should I make the assumption as stated in 1)? Otherwise the change of entropy of the universe would be 0, right?