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Evaluation of work in thermodynamics

  • Thread starter DottZakapa
  • Start date
  • #1
150
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Inside a cylinder with a sliding piston, n mole of monoatomic ideal gas at temperature TA occupy a volume VA at pressure PA, in equilibrium. The piston is expanded very slowly, turning the pressure in such a way that the product V⋅P2 remains constant till the volume VB .

I have to evaluate the work in the transformation from A to B:
VB = 4 VA
PA and VA are known

wAB = ∫ P⋅dV =

My question is:
- Which value of Pressure shall I insert instead of P considering the fact that it isn't constant during the transformation?
 

Answers and Replies

  • #2
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If VP2 remains constant, it must be equal to VP2 in state A. Can you write an equation to express this in terms of PA and VA?

Chet
 
  • #3
Doc Al
Mentor
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My question is:
- Which value of Pressure shall I insert instead of P considering the fact that it isn't constant during the transformation?
Express P as a function of V.
 
  • #4
150
7
VA⋅PA2=VB⋅PB2
Then
PA=(VB½⋅PB)/VA½
and then I substitute in the integral:
∫ (VB½⋅PB)/VA½ dV

is it ?
 
  • #5
20,209
4,249
VA⋅PA2=VB⋅PB2
Then
PA=(VB½⋅PB)/VA½
and then I substitute in the integral:
∫ (VB½⋅PB)/VA½ dV

is it ?
Not exactly. VP2=VAPA2

Solve for P and then integrate PdV between VA and VB.
 
  • #6
150
7
Aw ok! now i get it.
Thank you very much for your time. Very helpful.
Have a nice day : )
 

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