Category: 1. Reaction Equilibria

17.1. For their homework assignment three students, Julie, John, and Jacob, were working on the formation of ammonia. The feed is a stoichiometric ratio of nitrogen and hydrogen at a particular T and P. Julie, who thought in round numbers of product, wrote: John, who thought in round numbers of nitrogen, wrote: N2 + 3H2  2NH3 Jacob, who thought in round…

P17.1. An equimolar mixture of H2 and CO is obtained by the reaction of steam with coal. The product mixture is known as “water-gas.” To enhance the H2 content, steam is mixed with water-gas and passed over a catalyst at 550°C and 1 bar so as to convert CO to CO2 by the reaction: Any unreacted H2O is subsequently…

We have greatly enlarged the scope of our coverage of engineering thermodynamics with very little extension of the conceptual machinery. All we really did conceptually was recall that the Gibbs energy should be minimized. The provision that atoms can be moved from one chemical species to another with commensurate changes in energy and entropy simply…

It is not difficult to imagine situations in which reactions take place in the presence of multiple phases. Absorption of CO2 into NaOH solution involves a reaction of the CO2 as it dissolves to form sodium bicarbonate and sodium carbonate. Hydrogen bonding in “pure” fluids implies reaction and phase equilibrium at saturation conditions. The production of methyl…

Frequently chemical engineers must model chemical reactions without information on the Gibbs energy of formation. Although it can be estimated, often a better method is to conduct experiments to find equilibrium conditions and calculate Ka directly from compositions. Experiments can be performed over a temperature range, resulting in an empirical representation of Eqn. 17.28. In fact, methods like…

A remarkably simple technique can be applied to solve for the equilibrium compositions of species. It is most effective when only a gas phase is present. This technique recognizes the simplicity of the fundamental problem of minimizing the Gibbs energy at equilibrium. By expressing the total Gibbs energy of the mixture in terms of its…

When introducing entropy and reversibility in Section 4.11 on page 175, we made a general statement that spontaneous reactions generate entropy. Then, in Section 4.12 on page 177 we derived relations between availability and entropy generation. In that section, we treated a single nonreactive stream. For a reaction in a steady-state open system, Eqn. 4.54 becomes Bout = Hout – ToSout and Bin = Hin – ToSin involve H and S evaluated at the respective Tout and Tin. Enthalpies of mixed streams…

We have avoided discussing rate effects until now with the rationale that most coverage for reaction kinetics will occur in a course focused on reactor design. Nevertheless, there is overlap between the topics of reaction equilibria and reaction rates that can serve as a bridge between the two subjects. In all equilibrium phenomena, it is…

When a solid component is involved in a reaction, the fugacity ratio for activity in Eqn. 17.15 is typically expressed using activity coefficients. For a solid solution, where P is expressed in bar, Psat represents the solid sublimation pressure, and the Poynting correction is often negligible. Commonly, multiple solids exist as physical mixtures of pure crystals as discussed in Section 14.10 on page 556.…

When a liquid component is involved in a reaction, the fugacity ratio for activity in Eqn. 17.15 is typically expressed using activity coefficients. Thus, where P is expressed in bar, and the Poynting correction is often negligible, as shown. Another important change in working with liquid components is that in determining Ka liquid phase values are used for , not the ideal…