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Lairix

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## Homework Statement

10 moles of an ideal gas Cv = 20.8 J/mol at T0 = 300 K and P0 =0.3 MPa occupy the left half of an insulated vessel. At time t=0 a 1 kW electrical heating element is turned on. after 30 s, the partition dividing the vessel ruptures and the heating element is turned off. Calculate a) the final temperature Tf and pressure Pf of the gas in the vessel and b) the entropy change of the gas during the process.

## Homework Equations

PV= nRT

du = TdS - PdV

delta U = Q+ W

## The Attempt at a Solution

[/B]1 kw = 1 kJ/s

1 kJ/s x 30 s = 30 kJ

delta U = Q+ W -----> Q= 0 because system is insulated therefore delta U = W

30 kJ is the total amount of internal energy added to system

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My friend and I were attempting the solution this way. However, our textbook has set W=0 for some reason, and said that deltaU = n*Cv*delta(T) =Q.

We don't understand how W= 0 unless we assume that the gas is expanding against a vacuum which wasn't stated explicitly. ...Also, how is Q not equal to zero is the system is insulated ?