$3\mathrm{.}23.4\mathrm{.}00L$ of $Ar$ and $2\mathrm{.}50L$ of $He,$ each at $298K$ and $1\mathrm{.}50$atm, were mixed isothermically and isobarically. The mixture was then expanded to a final volume of $20\mathrm{.}0L$ at $298K.$ Write chemical reactions for each step, and determine the change in entropy for the complete process.