Effects of Gauss–Bonnet entropy on thermodynamics of Kiselev black hole

In this paper, the thermodynamics of Reissner–Nordström-anti de Sitter black hole surrounded by quintessence is studied and the impact of the Gauss–Bonnet term is measured. The modified entropy, first law of thermodynamics and corresponding Smarr relation are derived due to the combined action of the Gauss–Bonnet term and quintessence fluid. We study the so-called black hole chemistry from the analysis of the corresponding equation-of-state, conjugate potential and the critical points in the extended phase space. To study the phase transitions, we plotted [Formula: see text], [Formula: see text] and [Formula: see text] diagrams and analyzed the conditions for the coexistence of phases.

Phase Transitions

At a phase transition two or more different phases may coexist, such as vapour and liquid. Phase transitions can be classified according to their order. A phase transition is of first order if going from one phase to the other involves a discontinuous change in entropy, and, thus, a finite amount of latent heat; higher-order phase transitions do not involve latent heat but exhibit other types of discontinuities. This chapter investigates the necessary conditions for the coexistence of phases, and how phases are represented in a phase diagram. The order of a phase transition is defined with the help of the Ehrenfest classification. The chapter discusses the Clausius–Clapeyron relation which, for a first-order phase transition, relates the discontinuous changes in entropy and volume. Finally, this chapter considers the Ising ferromagnet as a simple model which exhibits a second-order phase transition. It also introduces the notion of an order parameter.