In the following take 
and 
for nitrogen gas:
(a) Three pound moles of nitrogen at 70(°F), contained in a rigid vessel, is heated to 350(°F). How much heat is required if the vessel has a negligible heat capacity? If it weighs 200(lbm) and has a heat capacity of 
, how much heat is required?
(b) Four pound moles of nitrogen at 400(°F) is contained in a piston/cylinder arrangement. How much heat must be extracted from this system, which is kept at constant pressure, to cool it to 150(°F) if the heat capacity of the piston and cylinder is neglected?
a. For this constant-volume process, we have (neglecting the heat capacity of the vessel)
If we add in the heat capacity of the vessel, then we have
(as is likely to be the case in real life, the heat capacity of the vessel is greater than that of the gas).
b. For this constant-pressure process, we have (neglecting the heat capacity of the piston and cylinder)
We must extract 7000 Btu from the system.
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