Air in a piston$-$cylinder assembly undergoes a process from state $1,$ where $T_1=300K,p_1=100$kPa, to state $2,$ where $T_2=500K,p_2=650$kPa. Using the ideal gas model for air, determine the change in specific entropy between these states, in $K\frac{J}{k}g*K,$ if the process occurs $($a$)$ without internal irreversibilities, $($b$)$ with internal irreversibilities.