Energy diagrams, potential

The difference between the potential energies of products and reactants gives the heat of reaction. 

The difference between activation energy of forward reaction (E ) and activation energy of reverse reaction (E ) also gives the heat of a reaction. 

If the potential energy diagram above is given for the reaction, 

Draw the potential energy diagram for a reaction whose potential energy of products is 2 kJ, the activation energy for the reverse reaction is 45 kJ, and its AH (enthalpy) is -30 kJ. 

If the enthalpy of this reaction is 54 kJ, what would be the activation energy of the reverse reaction  

Since transition states cannot be directly observed, there is no experimental 

The temperature dependence of chemical reactions can be evaluated by considering the thermodynamic significance of Eq. 4.4, which gives 

Since AG = AH — T A5, separation of the enthalpy and entropy terms gives 

The term (KkT/h) varies only slightly with T compated to e because 

A plot of In (kr/ T) versus (1/ T) is then a straight line, and its slope is-AH /R. Once AH is determined in this manner, A5 is available from the relationship 

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Fig. VIII-5. Schematic potential energy diagram for electrons in a metal with and without an applied field , work function Ep, depth of the Fermi level. (From Ref. 62.)...

Figure A3.10.17 Potential energy diagram for the dissociative adsorption of N2 [46].

Figure C2.7.1. Schematic potential energy diagram for tire catalytic syntliesis and decomposition of ammonia on iron. The energies are in kJ mol tire subscript ads refers to species adsorbed on iron [i].

FIGURE 3 4 Potential energy diagram for rotation about the carbon-carbon bond in ethane Two of the hydrogens are shown in red and four in green so as to indicate more clearly the bond rotation... 

FIGURE 3 7 Potential energy diagram for rotation around the central carbon-carbon bond in butane... 

A potential energy diagram for nng inversion m cyclohexane is shown m Figure 3 18 In the first step the chair conformation is converted to a skew boat which then proceeds to the inverted chair m the second step The skew boat conformation is an inter mediate in the process of ring inversion Unlike a transition state an intermediate is not a potential energy maximum but is a local minimum on the potential energy profile... 

Sketch an approximate potential energy diagram similar to that shown in Figures 3 4 and 3 7 for rotation about the carbon-carbon bond in 2 2 dimethylpropane Does the form of the poten tial energy curve of 2 2 dimethylpropane more closely resemble that of ethane or that of butane" ... 

FIGURE 4 7 Potential energy diagram for proton transfer from hydrogen chio ride to tert butyl alcohol... 

Like tert butyloxonium ion tert butyl cation is an intermediate along the reaction pathway It is however a relatively unstable species and its formation by dissociation of the alkyloxonium ion is endothermic Step 2 is the slowest step m the mechanism and has the highest activation energy Figure 4 8 shows a potential energy diagram for this step... 

Step 3 IS bimolecular because two species the carbocation and chloride ion react together Figure 4 10 shows a potential energy diagram for this step... 

Potential Energy Diagrams for Multistep Reactions The SnI Mechanism... 

POTENTIAL ENERGY DIAGRAMS FOR MULTISTEP REACTIONS THE Sn1 mechanism... 

FIGURE 4 12 Potential energy diagram for the reaction of tert butyl alcohol and hydrogen chloride according to the SnI mechanism... 

Sketch a potential energy diagram for the reaction of 1 heptanol with hydrogen bromide paying careful attention to the positioning and structures of the intermediates and transition states... 

Section 4 9 The potential energy diagrams for separate elementary steps can be merged into a diagram for the overall process The diagram for the reac tion of a secondary or tertiary alcohol with a hydrogen halide is charac terized by two intermediates and three transition states The reaction is classified as a ummolecular nucleophilic substitution, abbreviated as SnI... 

If the Lewis base ( Y ) had acted as a nucleophile and bonded to carbon the prod uct would have been a nonaromatic cyclohexadiene derivative Addition and substitution products arise by alternative reaction paths of a cyclohexadienyl cation Substitution occurs preferentially because there is a substantial driving force favoring rearomatization Figure 12 1 is a potential energy diagram describing the general mechanism of electrophilic aromatic substitution For electrophilic aromatic substitution reactions to... 

FIGURE 12 1 Potential energy diagram for elec trophilic aromatic substitu tion... 

Shape of potential energy diagram is identical with that for ethane (Figure 3 4) Activation energy for rotation about the C—C bond is higher than that of ethane lower than that of butane... 

Potential energy diagram (Section 4 8) Plot of potential en ergy versus some arbitrary measure of the degree to which a reaction has proceeded (the reaction coordinate) The point of maximum potential energy is the transition state Primary alkyl group (Section 2 13) Structural unit of the type RCH2— in which the point of attachment is to a pnmary carbon... 

Fig. 12. Schematic potential energy diagram illustrating the changes associated with the individual reaction steps in CO oxidation on Pd (71).

Flocculation a relatively reversible aggregation often associated with the secondary minimum of a potential energy diagram. Particles are held together loosely with considerable surface separations. 

Fig. 3.3. Potential energy diagram for rotation about C(2)—C(3) bond of n-butane.

Reaction coordinate for a two-step reaction Fig. 4.1. Potential energy diagrams for single-step and two-step reactions. 

Fig. 4.3. Some typical potential energy diagrams that illustrate the application of Hammond s postulate.

The ionization mechanism for nucleophilic substitution proceeds by rate-determining heterolytic dissociation of the reactant to a tricoordinate carbocation (also sometimes referred to as a carbonium ion or carbenium ion f and the leaving group. This dissociation is followed by rapid combination of the highly electrophilic carbocation with a Lewis base (nucleophile) present in the medium. A two-dimensional potential energy diagram representing this process for a neutral reactant and anionic nucleophile is shown in Fig. 

The concept of ion pairs in nucleophilic substitution is now generally accepted. Presumably, the barriers separating the intimate, solvent-separated, and dissociated ion pairs are quite small. The potential energy diagram in Fig. 5.4 depicts the three ion-pair species as being roughly equivalent in energy and separated by small barriers. 

Fig. 5.5. Potential energy diagrams for substitution mechanisms. A is the S l mechanism. B is the Sjy2 mechanism with intermediate ion-pair or pentacooidi-nate species. C is the classical S).(2 mechanism. [Reproduced from T. W. Bentley and P. v. R. Schleyer, Adv.

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