  CO2 has attracted considerable attention in the recent years due to its role
in the greenhouse effect and environmental management. While its reaction with
water has been studied extensively, the same cannot be said for reactivity in
supercritical CO2 phase, where the conjugate acid/base equilibria proceed
through different mechanisms and activation barriers. In spite of the apparent
simplicity of the CO2 + H2O reaction, the collective effect of different
environments has drastic influence on the free energy profile. Enhanced
sampling techniques and well-tailored collective variables provide a detailed
picture of the enthalpic and entropic drivers underscoring the differences in
the formation mechanism of carbonic acid in the gas, aqueous and supercritical
CO2 phases.
