One mole of an ideal monoatomic gas expands isothermally against constant external pressure of 1 atm from initial volume of 1L to a state where its final pressure becomes equal to external pressure. If initial temperature of gas is 300K then total entropy change of system in the above process is:

`[R=0.082L atm mol^(-1) K^(-1)-=8.3J mol^(-1) K^(-1)]`