  Mass of a baryon as a function of temperature is calculated using
colour-singlet partition function for massless quarks (with two flavours) and
abelian gluons confined in a bag with a temperature dependent bag pressure
constant $B(T)$. The non-perturbative aspect of QCD interaction is included
through colour-singlet restriction on quark-gluon partition function in a
phenomenological way. The entropy bound inequality $ S/E \ \leq \ 2\pi R/\hbar
c $, where $S, \ E $ and $R$ are entropy, energy and radius, respectively of
the enclosed system with $\hbar c \ = \ 197.331 $ MeVfm, is found to be
consistent with the equilibrium solutions of the baryon mass upto a temperature
$T_E$. There is a region of temperature $T_E < T < T_C$ ($T_C$ is critical
temperature for quark-gluon plasma formation) in which no admissible
equilibrium states exist for the bag. We say that the system expriences a phase
jump from hadron to quark-gluon plasma through thermodynamic non-equlibrium
processes.
