It is stated that the change in entropy of an isolated system during an irreversible process is > 0; while for a reversible process, it is = 0. An isochoric process has a change in entropy given by : nCv(Pf/Pi). Does this mean that it is an irreversible process? ARen't isochoric processes reversible? (I don't know if there are 'other' types of isochoric processes... I've only studied one, which is the one studied in high school). Is it because the expression represents the change in entropy of a system and its surroundings; and hence, the initial statement still applies i.e. that the entropy of the isolated system is = 0 for a reversible process. Or is it something else entirely? I just need someone to clarify for me please. Won't take too long Thanks.