Q- A spherical tank contains 1 mole of helium gas at 10 bar and 300 K. The gas is slowly released to the atmosphere in such a way the remaining gas is maintained at constant total energy U. Heating or cooling may be used to keep U constant during the venting. Helium behaves as an ideal gas with a constant Cv =12.6 J/mol.K. The base state is that the specific energy, U, is zero at 300 K. When one-half of the helium has been vented, what is the temperature and pressure of the residual helium? 

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