This study attempts to combine the principles of nonequilibrium thermodynamics and photoacoustic Fourier transform infrared (PAFT-IR) spectroscopic detection as utilized in the analysis of nonequilibrium processes in matter. Such processes as diffusion and glass transition temperatures in polymers are analyzed. It is shown that the nonequilibrium mass balance equation, which governs diffusion processes, and the nonequilibrium internal energy balance responsible for the photoacoustic detection can be correlated. As a result, the relationship between the concentration of diffusant molecules in time and the photoacoustic intensity as a function of concentration can be established. Analysis of a nonequilibrium nature of the thermal processes near glass transmission temperatures shows that thermal nonequilibrium relaxations can be described in terms of rate constants for which the weight fractions with various energies can be correlated to the temperature fluctuations in a photoacoustic experiment. In this case, the internal energy balance equation can be represented by a regular heat expression.