1. The problem statement, all variables and given/known data The question says: In a process involving n moles of an ideal gas , what is the entropy change of the system ? 2. Relevant equations ΔS=qrev/T=(ΔU-w)/T (I have used the chemistry's equation of 1st law of thermodynamics which has the -ve sign) 3. The attempt at a solution The answer given is that: nCvln(T2/T1)+nRln(V2/V1). I don't know how they are giving this answer. The second term seems to be originated from work done in isothermal conditions . But its not given that the process is an isothermal one. And the first term ...huh..I don't know where it came from. So what is the origin of this answer?