  We study the effect of a single, instantaneous starburst on the dynamical and
chemical evolution of a gas-rich dwarf galaxy, whose potential well is
dominated by a dark matter halo. We follow the dynamical and chemical evolution
of the ISM by means of an improved 2-D hydrodynamical code coupled with
detailed chemical yields originating from type II SNe, type Ia SNe and single
low and intermediate mass stars (IMS). In particular we follow the evolution of
the abundances of H, He, C, N, O, Mg, Si and Fe. We find that for a galaxy
resembling IZw18, a galactic wind develops as a consequence of the starburst
and it carries out of the galaxy mostly the metal-enriched gas. In addition, we
find that different metals are lost differentially in the sense that the
elements produced by type Ia SNe are more efficiently lost than others. As a
consequence of that we predict larger [$\alpha$/Fe] ratios for the gas inside
the galaxy than for the gas leaving the galaxy. A comparison of our predicted
abundances of C, N, O and Si in the case of a burst occurring in a primordial
gas shows a very good agreement with the observed abundances in IZw18 as long
as the burst has an age of $\sim 31$ Myr and IMS produce some primary nitrogen.
However, we cannot exclude that a previous burst of star formation had occurred
in IZw18 especially if the preenrichment produced by the older burst was lower
than $Z=0.01$ Z$_{\odot}$. Finally, at variance with previous studies, we find
that most of the metals reside in the cold gas phase already after few Myr.
This result is mainly due to the assumed low SNII heating efficiency, and
justifies the generally adopted homogeneous and instantaneous mixing of gas in
chemical evolution models.
