One gram of saturated water vapour is enclosed in a thermally insulated cylinder ubder a weightless piston. The outside pressure being standard, `m = 1.0 g` of water is introduced into the cylinder at a temperature `t_0 = 22 ^@C`. Neglecting the heat capacity of the cylinder and the friction of the piston against the cylinder's walls, find the work performed by the force of the atmospheric pressure during the lowering of the piston.

Explanation

A quantity `(mc(T - T_0))/(q)` of saturated vapour must vapour must condense to heat the water to boiling point `T = 273^@K`
(Here `c` = specific heat of water, `T_0 = 295 K` = initial water temperature).
The work done in lowering the piston will then be
`(mc(T - T_0))/(q) xx (RT)/(M) = 25 J`,
since work done per unit mass of the condensed vapour is `pV = (RT)/(M)`.