Author: admin

Recall Eqn. 17.25, which we refer to as the general van’t Hoff equation: We can make rapid estimates of the equilibrium constant when we make the approximation that ΔHTo is independent of temperature. That is, suppose ΔCP = Δa = Δb = Δc = Δd = 0, which means the sensible heat effects for the reactants and products are the same. This is most…

Always remember that  depends on the standard state, which changes with temperature. Comparing Examples 17.2 and 17.3,  at 298 K (Ka = 1E-14), but decreases to  at 900 K (Ka = 0.242). In order to calculate , it may seem that we need to know ΔGfo for each compound at all temperatures. Fortunately this is not necessary because the  can be determined from the Gibbs energy…

In our preliminary examples, we have assumed rather idealized cases where none of the products are present in the inlet. However, in some cases, products may be present and then the reaction direction may not be as we anticipate. We can look at the reaction thermodynamics in a slightly different way to determine the direction…

At a given temperature, equilibrium values of the reaction coordinate are affected by pressure, inerts, and feed ratios. The principle that changing the quantities affects equilibrium conversions is known as Le Châtelier’s principle in honor of Henry Louis Le Châtelier who first characterized the phenomenon. An understanding of Le Châtelier’s principle is important for operating industrial reactions.…

The first term on the right side of Eqns. 17.12 and 17.16, , is called the standard state Gibbs energy of reaction at the temperature of the reaction, which we will denote . The standard state Gibbs energy of reaction is analogous to the standard state heat of reaction introduced in Section 3.6. The standard state Gibbs energy for reaction can be…

We now focus on the second summation of Eqn. 17.12. The ratio appearing in the logarithm is known as the activity, (cf. Eqns. 11.23 for a liquid, but now in a general sense):  activity The numerator  represents a mixture property that changes with composition. We have developed methods to calculate  in Eqns. 10.61 (ideal gases), 10.68 (ideal solutions), 11.14 (real solution using…

Several sub-steps are involved in the procedure outlined in Section 17.1 steps (1) and (2) to find the equilibrium constant. In this section, we derive the equilibrium constraint, and then show how the thermodynamic properties are used to simplify to Eqn. 17.1. At reaction equilibria, the total Gibbs energy is minimized. If the composition of a system is…

You have probably performed some reaction equilibrium computations before, usually in high school or freshman chemistry. This chapter shows how the “activities” (partial pressures for ideal gases) of products divided by reactants can be related to a quantity, Ka, that does not depend on pressure or composition, and despite its dependence on temperature, it is called…