Principle of Le Chatelier

The principle of Le Chatelier shows that when the pressure applied to a gaseous system is increased, dre equilibrium composition will chairge in order to reduce tire number of gaseous molecules. In the case of tire steam reforming of metlrane, the partial pressures of methane and steam will increase as the pressure is increased. In the water-gas reaction, where tire number of molecules is the same on both sides of the equation, the effect of increasing... 

According to the principle of Le Chatelier. the reaction should go back to the left to partially offset the increase in dichromate, which appears on the right side of Reaction 6-7. We can verify this algebraically by setting up the reaction quotient, Q. which has the same form as the equilibrium constant. The only difference is that Q is evaluated with whatever concentrations happen to exist, even though the solution is not at equilibrium. When the system reaches equilibrium, Q = K. For Reaction 6-7. 

In Chapter 16, we apply the fundamental general equilibrium expression to gaseous equilibrium reactions. In this chapter, we apply the same expression to the equilibria that involve weak acids and bases in aqueous solution, the principal difference being that all concentrations are expressed in moles/liter (rather than in atmospheres as for gases). All the general conclusions given in Chapter 16, and summarized in the principle of Le Chatelier, apply to equilibria in solutions as well as to those in gases. 

In cases of incomplete C,H acid deprotonation, an excess of base can be employed to increase the enolate fraction. According to the principle of Le Chatelier, the base excess increases the enolate fraction by a factor that equals the square root of the number of mole equivalents of the base employed. 

Barrett, Richard L. CO2-H2O Equilibrium and the Principle of Le Chatelier, J. Chem. Educ. 1959, 36, A741. 

This rule is a consequence of the principle of Le Chatelier, which has been discussed in the preceding chapter. If a system containing solute and solution is in equilibrium at a certain temperature, and the temperature is raised, the equilibrium will shift in such a way as to tend to restore the system to its original temperature, by the absorp tion of heat from the reaction. This shift will involve the transfer of more solute into the solution if the heat of solution is negative, or the reverse process if the heat of solution is positive. Consider a solid in equilibrium with its saturated solution at one temperature. Let... 

Explain, with use of the principle of Le Chatelier, why the color of nitrogen dioxide-tetroxide gas become a lighter red when the gas is compressed. 

Relation to the Principle of Le Chatelier. It can be seen that the equilibrium equation for the reaction corresponds to the principle of Le Chatelier. Let us consider an equilibrium state of the gas such that there are present nitrogen dioxide and dinitrogen tetroxide mole-... 

At 0° C [H+] and [OH ] are 0.83 X 10 , and at 100° C they are 6.9 X 10 . It is interesting that the change in amount of ionization with temperature corresponds (as, of course, it must) to the principle of Le Chatelier. When a solution of a strong acid and a solution of a strong base are mixed, a large amount of heat is given off. This shows that the reaction... 

The principle of Le Chatelier may now be stated as follows If a system is in stable equilibrium the increase in the intensity factor Xj., corresponding to a given increase dXj. in the quantity factor Xj., is smaller for a change to another state of stable equilibrium than for a change produced by altering Xr by dxr, while all the other quantity factors remain constant. 

The principle of Le Chatelier thus determines the direction in which a monovariant equilibrium is displaced under the influence of a change imposed on one of the variables by which its state is determined. We shall illustrate the application of this principle by a few examples. (For other examples see Khvolson, Lehrbuch, iii. p. 474.)... 

All cases to which the principle of Le Chatelier is applicable can be treated also by thermod3mamical methods. The principle of Le Chatelier is, however, usually much easier to apply, and is therefore of use whenever a knowledge of the direction of the displacement is all that is required. 

At 30 C, the solubility of calcium dithionate in water exceeds that of calcium sulfate by a factor of 105. According to the principle of Le Chatelier, under a high sulfur dioxide pressure the equilibrium of the given reaction lies on the right-hand side, while at a low pressure of sulfur dioxide essentially only calcium sulfate exists. This implies that when the digesters are depressurized, the high solubility of calcium sulfate is terminated, thus leading to calcium sulfate precipitation. 

The two examples discussed above show that the principle of Le Chatelier and Braun suffers from a number of important exceptions. Many workers have attempted to restate this principle in a completely general form but this form, if it exists at all, is necessarily very complex. It seems therefore more logical to discuss problems arising in... 

The specific examples in Section 14.5 illustrate how the law of mass action gives information about the nature of the equilibrium state. The law of mass action also explains and predicts the direction in which a reaction will proceed spontaneously when reactants and products are initially mixed together with arbitrary partial pressures or compositions. This requires a new concept, the reaction quotient Q, which is related to the equilibrium constant. Through the principle of Le Chatelier (described below), the mass action law also explains how a reaction in equilibrium responds to an external perturbation. 

FIGURE 14.13 Sketch of In K against 1/Tfor an exothermic reaction and for an endothermic reaction, as predicted by thermodynamics. Temperature increases to the left on this diagram. As T increases, K for the endothermic reaction increases and K for the exothermic reaction decreases in accordance with the principle of Le Chatelier. 

The principle of Le Chatelier states that when a change is placed on a system in equilibrium this will shift so as to reduce the effect of the change (quantities, pressure, temperature, etc.). Table 11.2 shows that, as predicted by the Le Chatelier principle, an increase in the pressure on this system increases the equilibrium ammonia concentration. 

It can be seen from these reaction equations that low steam excess can lead to critical conditions causing coke formation, according to the principle of Le Chatelier. 

Pressure affects a reaction system in two ways (1) reduction of the available molecular space, which has to do with conformation, and (2) increase of intrachain reactions (Hoover et al., 1989), which affect the d)mamics and reactions of biomolecules. The effect of HP on microbial inactivation, chemical or enzymatic reactions, and structural and /or functional properties of foods is based on the principle of Le Chatelier-Braun and on the State Transition Theory. 

The principle of Le Chatelier-Braun states that any reaction or phase transition, molecular transformation or chemical reaction that is accompanied by a volume decrease of the medium will be favored by HP, while reactions that involve an increase in volume will be inhibited. Qn the other hand, the State Transition Theory points out that the rate constant of a reaction in a liquid phase is proportional to the quasi-equilibrium constant for the formation of active reactants (Mozhaev et al., 1994 Bordarias, 1995 Lopez-Malo et al., 2000). To fully imderstand the dynamic behavior of biomolecules, the study of the combined effect of temperature and pressure is necessary. The Le Chatelier-Braim Principle states that changes in pressure and temperature cause volume and energy changes dependent on the magnitude of pressure and temperature levels and on the physicochemical properties of the system such as compressibility. "If y is a quantity characteristic of equilibrium or rate process, then the influence of temperature (7 and pressure (P) can be written as ... 

The Principle of Le Chatelier and Braun, or The Principle of Mobile Equilibrium ... 

The effect of pressure on a chemical equilibrium follows the principle of le Chatelier an increase in temperature shifts the equilibrium in the direction of highest enthalpy for an endothermic reaction, an increase in pressure in that of smallest volume. The relation giving the temperature effect is obtained by differentiating Eq. (7.3) at constant pressure, resulting in... 

It is easy to show by this type of argument that for any reaction, increasing the volume will cause a shift in the direction of producing more molecules. If the reaction is such that the number of species is the same on both sides of the equation, the volume cancels out in K, and changing the volume brings about no shift in equilibrium. These effects were predicted in 1884 by the principle of Le Chatelier. 

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