Ryan Mullen’s paper on using reaction ensemble Monte Carlo to compute absorption isotherms for CO2 in reactive ionic liquids has appeared in the Journal of Chemical Theory and Computation. In this paper, we show that one can get quantitative agreement with experiment for the absorption of CO2 into an aprotic heterocyclic anion ionic liquid using reaction ensemble Monte Carlo (RxMC) with the semigrand reaction move. Heats of absorption and reaction from both experiment and simulation are exothermic and of comparable magnitude. Replacing experimental Henry’s constants with their simulated counterparts improves the accuracy of a Langmuir-type model at moderate pressures. Nonidealities that affect chemical equilibrium are identified and calculated with high precision.