A vertical cylinder with a massless piston filled with one mole of an ideal gas. The piston can move freely without friction. The piston is slowly raised so that the gas expands isothermally at temperature 300 K. The amount of work done by external agent in increasing the volume two times in kJ is____.
 $(R=\frac{25}{3}J/mol/K,{\text{log}}_{\text{e}}\text{2 }=0.\text{7})$