Liquid-vapor flows with phase transitions have a wide range of applications.
Isothermal two-phase flows described by a single set of isothermal Euler
equations, where the mass transfer is modeled by a kinetic relation, have been
investigated analytically in (Quarterly of applied Mathematics, vol.\ LXXI 3
(2013), pp.\ 509-540.). This work was restricted to liquid water and its vapor
modeled by linear equations of state. The focus of the present work lies on the
generalization of the primary results to arbitrary substances, arbitrary
equations of state and thus a more general kinetic relation. We prove existence
and uniqueness results for Riemann problems. In particular, nucleation and
evaporation are discussed