Molecular dynamics (MD) simulations were conducted to calculate the binary mixture properties (excess molar heats and volumes) of 1-ethyl-3-methylimidazolium acetate [EMIM][Ac] with six polar covalent molecules (acetic acid, acetone, chloroform, dimethyl sulfoxide, isopropyl alcohol, and methanol) over the entire composition range. All of the binary mixtures of [EMIM] [Ac] with cosolvents reported negative volumes of mixing over the entire composition range while releasing heat (exothermic heats of mixing), except for the acetone mixture, which had miscibility issues at higher concentrations (x(acetone) >= 0.6). These results were attributed to the nature, size, and structure of the molecules as well as the nature of the interaction between the mixture components. Further, aggregation of the ionic liquid (IL) at higher concentrations of the cosolvent added to the above observed effects, except for the acetic acid mixture. These results have been interpreted in terms of hydrogen-bonding and intermolecular interactions among the binary mixture components via radial distribution functions. The results showed that hydrogen-bonding interactions between the IL and cosolvent play a major role in the volumetric and energetic properties of the mixtures. In the case of the acetic acid mixture, aggregation of acetic acid molecules is reported at lower concentrations of acetic acid (x(acetic) (acid) = 0.1), while [EMIM][Ac] molecules were completely solvated at higher concentrations of acetic acid (x(acetic) (acid) = 0.9). Mixtures of [EMIM][Ac] with methanol showed isolated methanol molecules at lower concentrations of methanol (x(methanol) = 0.1), whereas IL ions aggregated to form pairs at higher concentrations of methanol.