We recently developed a new class of smart solvents, which are reversible ionic liquids. Addition of CO2 to guanidine-alcohol or the amidine-alcohol solutions causes the formation of a room temperature ionic liquid which can easily be reversed by bubbling inert N2 or Ar, or by applying heat. Because of this “built-in” ability to undergo a step change in solvent properties, these liquids have extensive potential applications for sustainable processes. We establish the thermodynamics of the formation and reversal of these switchable ionic liquids by determining the reaction equilibrium constants and enthalpies of reaction. In addition we address the effect the structure of the alcohol and of the base, on the thermodynamic properties of the reversible ionic liquid. This knowledge will enable us to tailor these smart solvents for their use in plethora of sustainable applications.