Steady-State Approximation in Kinetics: Applying the Technique to Consecutive Reactions, Study Guides, Projects, Research of Chemistry

Download Steady-State Approximation in Kinetics: Applying the Technique to Consecutive Reactions and more Study Guides, Projects, Research Chemistry in PDF only on Docsity! Steady-state approximation • Equations representing kinetic networks of more than three states are not soluble analytically. • One means of pushing the techniques as far as possible using analytical solutions is to set the derivatives of intemediates equal to zero: d[Intermediate]/dt = 0 • To see when one can use this approximation we consider the effect of increasing the second rate constant relative to the first. Steady-state approximation • We start with k1 = 10 k2. [A](t) Initial [B](t) Intermediate [C](t) Final Steady-state approximation • And finally k1 = 1.1 k2. [A](t) Initial [B](t) Intermediate [C](t) Final Steady-state approximation • And finally k1 = 1.1 k2. [A](t) Initial [B](t) Intermediate [C](t) Final Note that the slope of the intermediate is approaching zero. Application of the steady-state approximation • The steady state approximation can be applied to the consecutive reaction scheme k1 k2 A → B → C. if the concentration of B is fairly constant. • The result of setting d[B]/dt = 0 is: k1[A] - k2[B] = 0 and d[C]/dt = k1[A]. Since d[A]/dt = - k1[A] we see that d[C]/dt = - d[A]/dt and [C]=(1 - exp{-k1t})