In a system not isolated from its
surroundings, the work done may be
different from the change in internal
energy. Moreover, the process is
spontaneous if overall the entropy of
the system and its surroundings increases.
In the process depicted here, the entropy
of the system decreases, so that of the
surroundings must increase in order for the
process to be spontaneous, which means
that energy must pass from the system to
the surroundings as heat. Therefore, less
work than ΔUcan be obtaine