Heat capacities of ionic liquids and their heats of solution in molecular liquids

Abstract Heat capacities of ionic liquids (IL): 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF 4 ), 1-ethyl-3-methyl imidazolium bis((trifluoromethyl)sulfonyl) imide (EMImN(CF 3 SO 2 ) 2 ), 1-bytyl-3-methylimidazolium tetrafluoroborate (BMImBF 4 ) and N , N -methyl, propyl pyrrolidinium bis((trifluoromethyl)sulfonyl) imide (MPPyN(CF 3 SO 2 ) 2 ) were measured from 283.15 to 358.15 K. Room temperature heat capacities have also been estimated by an additive group contribution method, based on the assumption that the heat capacity of a molecular compound equals the sum of individual atomic-group contributions. The C p 293.15 K estimated values are about 12% higher than experimental values. The estimates suggest that heat capacities of ionic liquids do not differ considerably from those typical for molecular liquids (ML). The heats of solution, Δ sol H , of ionic liquids EMImBF 4 , BMImBF 4 EMImN(CF 3 SO 2 ) 2 and MPPyN(CF 3 SO 2 ) 2 were measured in water, acetonitrile (AN) and methanol, as a function of ionic liquid concentration c m . The measured Δ sol H values decrease with decreasing c m . Enthalpies of ionic liquid transfer, Δ t H °, from water to methanol and acetonitrile were calculated from measured solution enthalpies. Values of Δ t H ° for the transfer from water to methanol are positive and those for the transfer to acetonitrile are negative.

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