Linear acoustics in gas mixtures with rate processes

Linear acoustics in an unbounded medium in which an arbitrary number of independent rate processes (chemical reactions and/or excitations on internal degrees of freedom) take place are dealt with. The medium is supposed to be in an initial quiescent and full equilibrium state and all diffusion processes are assumed to be negligible. (Linear acoustics without neglection of diffusion processes or in nonquiescent media and nonlinear acoustics with and without diffusion processes are not dealt with). The extremely simplified case dealt with is nonetheless very useful. It allows for the following: elucidation of the role played by a number of basic notions of thermodynamics such as equilibrium and stability; quantification of the 'response' of the media to small disturbances; and suggestion of diagnostic techniques which may be used to study the kinetics of rate processes and their couplings, and so forth. Equilibrium and nonequilibrium thermodynamics of composite systems as specialized to the subject case are considered. The field equations and their linearized form appropriate to the study of linear acoustics are addressed, as are the general features of linear acoustics, dispersion equation, and properties of the acoustic susceptibility.