Enthalpies of solution and partial molar volumes of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate were determined in 15 solvents of different polarity. Very large differences of the enthalpies of solution (ΔΔsolHIL=38.9 kJ⋅mol−1) and partial molar volumes (ΔVIL=43 cm3⋅mol−1) are nearly the same as observed for lithium perchlorate solutions. These results clearly indicate that the low values of the macroscopic polarity parameters of [bmim]BF4 do not correspond with the large differences of the intermolecular interactions in IL solutions. The values of the partial molar volume of the cation, \(V_{[\mathrm{bmim}]^{+}}\), were estimated for the first time. The changes of the partial molar volumes, VIL, reflect mainly the changes of anion volume, \(V_{\mathrm{BF}_{4}^{-}}\). The rate of the Diels–Alder reaction of 9,10-dimethylanthracene with maleic anhydride in the [bmim]BF4 medium was nearly the same as in common molecular solvents.