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hahaha158
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Homework Statement
A cylinder contains 0.2mol of Helium at 30 degrees C and is heated different ways.
How much heat is needed to raise the temperature to 70C while keeping thevolume constant?
Homework Equations
dQ=dU+dT
nCpdT=nCvdT+nRdT
The Attempt at a Solution
What I am confused about is whether to use the nCpdT (heat added) or nCvdT (change in internal energy). If it is a constant volume process, wouldn't that mean dQ=dU therefore nCpdT=nCvdT?
Obviously that is not the case as the moles (0.2) are constant as is the change in temperature (70-30=40C or 40K). As as result Cp=Cv which should be untrue for a monatomic gas.
What is the cause for this discrepancy and how can I determine which equation to use?
Thanks