One mole of helium is placed in a container at a pressure of 2 atmospheres and at a temperature of 300K. The gas is allowed to expand irreversibly and adiabatically to a pressure of 1 atm. Which of the following is true for this process? $(C_p=\frac{5}{2}R,\log 2=0.3,\log 5=0.7,\text{}R=2cal{k}^{-1}mo{l}^{-1})$