Modified by Jed Macosko

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Presentation transcript:

Modified by Jed Macosko Reaction Dynamics Potential Energy Modified by Jed Macosko 1/2/2019

Collision Theory 1 In the simple ________ __________ model of molecular collisions, the impact parameter (distance of closest approach) is the _______ of the radii of the collision pair. rA rB d = rA+rB Collision __________ area s collision volume swept by A per sec. Collision __________ collision frequency per A molecule number of collisions per unit time per unit volume = (m-3) (m-3) (m2) (m s-1)  m-3 s-1 Modified by Jed Macosko 1/2/2019

Modified by Jed Macosko Collision Theory 2 _______ where is the __________ mass. __________ Energy: Only a fraction of collisions have sufficient kinetic energy to overcome the activation barrier. molecules m-3 s-1 __________ Rate Constant mol m-3 s-1 L = Avogadro’s no. mol m-3 s-1 mol m-3 s-1 mol dm-3 s-1 mol-1 dm3 s-1 M-1 s-1 Modified by Jed Macosko 1/2/2019

Modified by Jed Macosko Collision Theory 3 Basic collision theory has several deficiencies, which can be partially overcome by making more sophisticated models. __________ Dependence The reactions of polyatomic molecules typically depend on their mutual orientation. Solution: Replace s with s*, the __________ cross-section: steric factor __________ Interactions Molecules are not incompressible hard spheres! rij u U(r) Hard sphere Square well __________ The collision energy depends on the impact parameter, which is angular dependent. There is no way to predict the activation energy. Modified by Jed Macosko 1/2/2019

Potential Energy Surfaces 1 A reaction ________ is a plot of the energy of a reaction system as a function of all the independent variables (bond ________ and bond _______). Even a collinear triatomic reaction such as A + BC  AB + C needs a 3-D plot: rA-B A + BC AB + C E rB-C rA-B or a contour plot: _________vibration of A-B-C minimum energy path rB-C Modified by Jed Macosko 1/2/2019

Potential Energy Surfaces 2 Modified by Jed Macosko 1/2/2019

__________ State Theory (TST) Assume that in the course of a reaction there is some __________ surface (point on a one-dimensional reaction path) past which reaction to products is inevitable. Assume that this __________ state is in effective equilibrium with the reactants. reactants products U reaction coordinate kp K‡ A full discussion of kp and K‡ requires quantum chemistry and statistical mechanics, and leads to the ________ Equation transmission coefficient or tunneling factor Modified by Jed Macosko 1/2/2019

Thermodynamic Formulation of TST For gases, where Substitute into the Eyring Equation: “hide” k in the DS factor Since (for gases only) Modified by Jed Macosko 1/2/2019