## Appendix A: entropy for a mixture of perfect gases and radiationFrom basic physics, the entropy of a mixture of perfect gases in molar fraction is given by with where for the ions of species for the electrons with the assumption of complete ionisation. We
call Let us consider a mixture of hydrogen, helium and metals in
respective mass fractions with We identify the heavy elements with oxygen and the corresponding molar fraction is thus . For the sake of consistency, we must also take For a binary mixture with only H and He, we get For a mixture of perfect gases and radiation, we are looking for an expression of the form with We have for one mole At constant For variable We see that the entropy changes also depend on the changes of
© European Southern Observatory (ESO) 1998 Online publication: June 2, 1998 |