where 𝐴 is the pre-exponential factor, 𝐸 𝑎 is the activation energy, and 𝑅 is the universal gas constant. The Arrhenius equation assumes a linear relationship between ln 𝑘 and 1∕𝑇 and treats 𝐴 and 𝐸 𝑎 as temperature-independent parameters. While most reactions show the linear dependence, many liquid phase reactions start to exhibit non-Arrhenius behavior as temperature approaches a critical point of a solvent . Near a critical point, the physicochemical properties of a solvent change dramatically with a slight variation of temperature, and as a result, rapid slowing-down or acceleration of rate constants are observed for many liquid phase reactions at elevated temperatures. A modified version of the Arrhenius equation is frequently used to describe more complex temperature dependence of a rate constant: