Spontaneous processes evacuated space

A FIGURE 19.2 Expansion of a gas into an evacuated space is a spontaneous process. The reverse process—gas molecules initially distributed evenly in two flasks all moving into one flask—is not spontaneous. 

A Figure 19.2 Expansion of a gas into an evacuated space is a spontaneous process. 

Now let s consider another example, the expansion of an ideal gas at constant temperature (referred to as an isothermal process). In the cylinder-piston arrangement of Figure 19.5, when the partition is removed, the gas expands spontaneously to fill the evacuated space. Can we determine whether this particular isothermal expansion is reversible or irreversible Because the gas expands into a vacuum with no external... 

A Figure 19.5 Expansion of an ideal gas into an evacuated space is spontaneous. In (a) flask B holds an ideal gas at 1 atm pressure and flask A is evacuated. In (b) the stopcock connecting the flasks has been opened. The ideal gas expands to occupy both flasks A and B at a pressure of 0.5 atm. The reverse process is not spontaneous. 

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