The Chemistry of Black Holes

I provide a short overview of black hole thermodynamics in extended phase space, where the cosmological constant is interpreted as thermodynamic pressure. This leads to an understanding of black holes from the viewpoint of chemistry, in terms of concepts such as Van der Waals fluids, reentrant phase transitions, and triple points. I discuss first the motivations for the extended phase space, indicating why the mass of a black hole should be understood as the analogue of thermodynamic enthalpy. I think go on to describe how charged and rotating black holes exhibit novel chemical-type phase behaviour, hitherto unseen.