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kcband
Joined: 20 Feb 2012 Posts: 1 Location: seattle

Posted: Mon Feb 20, 2012 9:19 pm Post subject: thermodynamics graph problem 


Look at the graph and answer the questions below. The graph of pressure P versus V shows the expansion of 2.0 moles of a monatomic ideal gas from state A to state B. Pa=Pb=600N/m^2, Va = 3.0m^3 and Vb = 9.0m^3.
1. Calculate the work done BY THE GAS as it expands.
2.Calculate the change in internal energy of the gas as it expands.
3.Calculate the heat added to or removed from the gas during this expansion.
Any help would be great thanks. 

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hepcj Site Admin
Joined: 23 Jun 2007 Posts: 125

Posted: Tue Feb 21, 2012 12:13 am Post subject: 


These questions are an application of the first law of thermodynamics.
dU = dQ  dW (1)
or change in internal energy = heat input  work out
Work done by gas is:
W = P dV
=> W = P [Vf  Vi]
This expansion is at constant pressure therefore dU =0.
Therefore from (1), dQ = dW. or the heat is added to the system is equal to the work done. 

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