where X is the descriptor value and H j is the enthalpy of adsorbate j. Considering that X is calculated through a large set of ordinary di↵erential equations or di↵erential-algebraic equations, and the system includes the forward rate constants k and species enthalpies H as parameters, X in Equation 14 can be expressed as X(k, H, . . .). If k(H) is also a function of H, then using the chain rule, the partial derivative of X with respect to H j is: