College Physics (4th Edition)

The total internal kinetic energy is $3405~J$
The total internal kinetic energy is the number of molecules $N$ multiplied by the average kinetic energy of the molecules $\overline{KE}$. We can find the total internal kinetic energy: $N\times~\overline{KE} = \frac{3}{2}~NkT$ $KE = \frac{3}{2}~NkT$ $KE = \frac{3}{2}~(6.022\times 10^{23})(1.38\times 10^{-23}~J/K)(273.15~K)$ $KE = 3405~J$ The total internal kinetic energy is $3405~J$.