Catalysts potential energy diagram

To see how the catalyst accelerates the reaction, we need to look at the potential energy diagram in Fig. 1.2, which compares the non-catalytic and the catalytic reaction. For the non-catalytic reaction, the figure is simply the familiar way to visualize the Arrhenius equation the reaction proceeds when A and B collide with sufficient energy to overcome the activation barrier in Fig. 1.2. The change in Gibbs free energy between the reactants, A -r B, and the product P is AG. 

Figure 1.2. Potential energy diagram of a heterogeneous catalytic reaction, with gaseous reactants and products and a solid catalyst. Note that the uncatalyzed reaction has to overcome a substantial energy barrier, whereas the barriers in the catalytic route are much lower.

Note that in the latter step the adsorption sites on the catalyst are liberated, so that these become available for further reaction cycles. Figure 1.5 shows the reaction cycle along with a potential energy diagram. 

Several text books introduce the concept of catalysis with a potential energy diagram in which an energy barrier separates the products and the reactants, and then state that a catalyst lowers this barrier. Do you approve of this representation Explain your answer. 

Figure 16-15 Potential energy diagrams showing the effect of a catalyst. The catalyst provides a different mechanism, corresponding to a lower-energy pathway, for the formation of the products. A catalyzed reaction typically occurs in several steps, each with its own barrier, but the overall energy barrier for the net reaction,, is lower than that for the uncatalyzed reaction, E. The value of depends only on the states of the reactants and products, so it is the same for either path.

Fig. 8. One-dimensional potential energy diagram for the adsorption and dissociation of oxygen on an Ag catalyst after Dean and Bowker, 1989).

Sketch a potential energy diagram for a reaction that shows the effect of a catalyst on an exothermic reaction. 

In order to understand how a catalyst can accelerate a reaction a potential energy diagram should be considered. 

A potential energy diagram showing how a catalyst works by giving alternative energy pathways in a reaction. 

Figure 3.1 Generic potential energy diagram showing the effect of a catalyst in a hypothetical exothermic chemical reaction X + Y to give Z.

Draw a potential-energy diagram for an uncatalyzed exothermic reaction. On the same diagram, indicate the change that results on the addition of a catalyst. Discuss the role of a catalyst in changing the rate of reaction. 

Figure 5.11. Potential energy diagram for ammonia synthesis on a promoted iron catalyst.

Fig.1 Calculated free energy diagram for hydrogen evolution at a potential U = 0 V relative to the standard hydrogen electrode at pH = 0. The free energy of H+ + e is by definition the same as that of j - i at standard conditions. The free energy of H atoms bound to different catalysts is then found by calculating the free energy with respect to molecular hydrogen including zero-point energies and entropy terms (reprinted from Ref 83 with permission).

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