# Evaluation of work in thermodynamics

1. Sep 8, 2015

### DottZakapa

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?

2. Sep 8, 2015

### Staff: Mentor

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. Sep 8, 2015

### Staff: Mentor

Express P as a function of V.

4. Sep 8, 2015

### DottZakapa

VA⋅PA2=VB⋅PB2
Then
PA=(VB½⋅PB)/VA½
and then I substitute in the integral:
∫ (VB½⋅PB)/VA½ dV

is it ?

5. Sep 8, 2015

### Staff: Mentor

Not exactly. VP2=VAPA2

Solve for P and then integrate PdV between VA and VB.

6. Sep 8, 2015

### DottZakapa

Aw ok! now i get it.
Thank you very much for your time. Very helpful.
Have a nice day : )