In this article we propose an irreversible adiabatic expansion model, modified from previous work,
to explain the fog bottle experiment. Our model divides the phenomenon into five thermodynamic
states, and we include in our calculation irreversible work pushing a stopper out of the bottle and
heat gain from the condensation of saturated vapour. In the experiment, thermodynamic variables
including pressure and temperature as functions of time were measured. The work done in pushing the
stopper out was measured and the condensation heat was determined using the Clausius–Clapeyron
equation to determine saturated vapour pressure. As a result, fog formation was explained through a
phase diagram of water showing the saturated vapour pressure during irreversible adiabatic
expansion. Also, state variables ( P , V and T ) and the entropy change of the real process were
compared with the reversible and irreversible adiabatic expansion and our modified process. Using a