TST is used primarily to understand qualitatively how chemical reactions take place. TST has been less successful in its original goal of calculating absolute reaction rate constants because the calculation of absolute reaction rates requires precise knowledge of potential energy surfaces, but it has been successful in calculating the standard enthalpy of activation (Δ"H"‡, also written Δ‡"H"ɵ), the standard entropy of activation (Δ"S"‡ or Δ‡"S"ɵ), and the standard Gibbs energy of activation (Δ"G"‡ or Δ‡"G"ɵ) for a particular reaction if its rate constant has been experimentally determined. (The ‡ notation refers to the value of interest "at the transition state"; Δ"H"‡ is the difference between the enthalpy of the transition state and that of the reactants.)