Piston sweep

Condition 2 Figure 12-12. Start of gas discharge from cylinder. Gas has slightly exceeded the system pressure, and the discharge valve opens releasing gas to the system. The piston begins to sweep the gas from the cylinder as it moves toward condition 3. 

Sweep most of the air out with a stream of butane and insert the piston to the liquid level butane in the headspace dissolves in the organic phase. 

Insert the piston while sweeping out air with a stream of butane. 

Suppose that water at its normal boiling point (100 C or 73 K) is maintained in a cylinder that has a frictionless piston. The equilibrium pressure of the vapor will be 1 atm, and an external pressure of 1 atm must therefore be exerted on the piston in order to prevent it from moving. Suppose that we now reduce the external pressure by an infinitesimal amount in order to have a reversible expansion. We allow the piston to sweep out a volume of 2 dm, and want to calculate the work done by the system. 

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