A rigid tank with a volume of 0.75 m3 initially contains air at 70 kPa and 25 degrees C. A small hole develops in the tank. The surrounding air at 100 kPa and 25 degrees C slowly leaks into the tank due to the hole. Heat transfer between the surroundings and the tank maintains a constant air temperature of 25 degrees C inside the tank. Determine the heat transfer. When I did: m = (PV)/(RT) = (70 x 0.75)/(0.2870 x 298) = 0.614 kg and m = V / specific volume = 0.75 / 631.9 = 0.00119 kg (where the specific volume was found on table -17 of the Thermodynamics Tables http://imageshack.us/photo/my-images/265/unledky.png/ ), the results don't match each other. I assumed air was an ideal gas because pressure was low, temperature was high, compared to its critical point values. The error that was involved is big. Anyone know why?