Spontaneous adiabatic expansion or compression

Section 3.4.1 explained that during a rapid spontaneous expansion of the gas in the cylinder shown in Fig. 3.4, the pressure pb exerted by the gas at the moving piston is less than the pressure at the stationary wall. Consequently the work given by u = — f Ph dE is less negative for a spontaneous adiabatic expansion than for a reversible adiabatic expansion with the same initial state and the same volume change. 

These observations are summarized by the statement that, for an adiabatic expansion 

Thermodynamics and Chemistry, second edition, version 3 2011 by Howard DeVoe. Latest version www.chem.umd.edu/thermobook 

---