Enthalpy profile diagrams

The enthalpy profile diagrams for an uncatalysed and a catalysed reaction are shown in Figure 2.11. 

We can draw enthalpy profile diagrams (also known as reaction pathway diagrams) to show enthalpy changes. The enthalpy of the reactants and products is shown on they-axis. The x-axis shows the reaction pathway, with reactants on the left and products on the right. 

For an exothermic reaction, energy is released to the surroundings. So the enthalpy of the reactants must be greater than the enthalpy of the products. We can see from the enthalpy profile diagram for the combustion of methane (Figure 6.3) that - H eactants negative. 

Figure 6.3 Enthalpy profile diagram for the combustion of methane.

Represent these changes on an enthalpy profile diagram. [3]... 

The activation energy for an exothermic reaction and an endothermic reaction can be shown on enthalpy profile diagrams, as shown in Figures 9.4 and 9.5. 

The activation energy of a reaction is the minimum energy required by colliding particles for a reaction to occur. Enthalpy profile diagrams show how the activation energy provides a barrier to reaction. 

Mac et al. (1967). The results are of interest because they show the effect of solvent on two 8 2 reactions of different charge type, but which pass through the same transition state. Enthalpy and entropy profile diagrams for reaction (31) in DMAC are in Fig. 2. 

Fig. 7.57 A schematic diagram of cathode events for SOFC fuel cells. The processes actually taJdng place are usually much more complicated (cf. Sections 6.7 and 7.3.3), the same applies to the free enthalpy profile (654). (Note that concerning gas diffusion (1) the configuration effect is included in the free enthalpy profile.) For simplicity smd in contrast to reaJity, it is assumed that the oxygen is completely ionized when it enters the electrolyte.

The mechanism of the reaction A - B consists of two steps, with the formation of a reaction intermediate. Overall, the reaction is exothermic, (a) Sketch the reaction profile, labeling the activation energies for each step and the overall enthalpy of reaction, (h) Indicate on the same diagram the effect of a catalyst on the first step of the reaction. 

To evaluate the true temperature difference (driving force) in a mixed vapour condenser a condensation curve (temperature vs. enthalpy diagram) must be calculated showing the change in vapour temperature versus heat transferred throughout the condenser, Figure 12.48. The temperature profile will depend on the liquid-flow pattern in the condenser. There are two limiting conditions of condensate-vapour flow ... 

Figure 6.9 Temperature profiles in the FEHE (a) longitudinal temperature profile and (b) temperature-enthalpy diagram.

The McCabe-Thiele diagram for this design, showing that the feed is to the optimum stage, is shown in Fig. 13-44. The flow profiles are shown in Fig. 13-45 note the step changes due to both the feed and the sidestream. As was the case in Example 3, the curvature in the flow profiles is due to enthalpy changes. 

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