A vessel, divided into two parts by a partition, contains one mol of oxygen gas (Cv=25R) at 75C and 30 bar on one side and four mol of argon gas (Cv=23R) at 130C and 20 bar on the other. The partition is removed and the gases mix adiabatically till temperature and pressure are uniform. Estimate the total change in entropy for the process assuming ideal gas. [13 marks]