Chatelier

Single reversible reactions. The maximum conversion in reversible reactions is limited by the equilibrium conversion, and conditions in the reactor are usually chosen to increase the equilibrium conversion. Le Chatelier s principle dictates the changes required to increase equilibrium conversion ... 

Le Chatelier s theorem or principle When a constraint is applied to a system in equilibrium, the equilibrium will lend to move in such a way as to neutralize the efferi of Hie constraint. Thus, e.g., in a reaction such as... 

Reaction (13.4) is exothermic and reversible, and begins at about 700 K by Le Chatelier s Principle, more iron is produced higher up the furnace (cooler) than below (hotter). In the hotter region (around 900 K), reaction (13.5) occurs irreversibly, and the iron(II) oxide formed is reduced by the coke [reaction (13.6)] further down. The limestone forms calcium oxide which fuses with earthy material in the ore to give a slag of calcium silicate this floats on the molten iron (which falls to the bottom of the furnace) and can bo run off at intervals. The iron is run off and solidified as pigs —boat-shaped pieces about 40 cm long. 

According to Le Chatelier s principle, a system at equilibrium adjusts so as to mini mize any stress applied to it When the concentration of water is increased the system responds by consuming water This means that proportionally more alkene is converted to alcohol the position of equilibrium shifts to the right Thus when we wish to pre pare an alcohol from an alkene we employ a reaction medium m which the molar con centration of water is high—dilute sulfuric acid for example... 

When esterification is the objective water is removed from the reaction mixture to encourage ester formation When ester hydrolysis is the objective the reaction is carried out m the presence of a generous excess of water Both reactions illustrate the applica tion of Le Chatelier s principle (Section 6 10) to organic synthesis... 

Le Chateliers principle (Section 6 10) A reaction at equilib rium responds to any stress imposed on it by shifting the equihbnum in the direction that minimizes the stress Lewis acid See acid Lewis base See base... 

The observation that a system at equilibrium responds to a stress by reequilibrating in a manner that diminishes the stress, is formalized as Le Chatelier s principle. One of the most common stresses that we can apply to a reaction at equilibrium is to change the concentration of a reactant or product. We already have seen, in the case of sodium acetate and acetic acid, that adding a product to a reaction mixture at equilibrium converts a portion of the products to reactants. In this instance, we disturb the equilibrium by adding a product, and the stress is diminished by partially reacting the excess product. Adding acetic acid has the opposite effect, partially converting the excess acetic acid to acetate. 

How might we solve equation 6.34 if we do not have access to a computer One possibility is that we can apply our understanding of chemistry to simpKfy the algebra. From Le Chatelier s principle, we expect that the large initial concentration of Pb will significantly decrease the solubility of Pb(I03)2. In this case we can reasonably expect the equiKbrium concentration of Pb to be very close to its initial concentration thus, the following approximation for the equilibrium concentration of Pb seems reasonable... 

Le Chatelier s principle provides a means for predicting how systems at equilibrium respond to a change in conditions. When a stress is applied to an equilibrium by adding a reactant or product, by adding a reagent that reacts with one of the reactants or products, or by changing the volume, the system responds by moving in the direction that relieves the stress. 

Le Chatelier s principle when stressed, a system that was at equilibrium returns to its equilibrium state by reacting in a manner that relieves the stress, (p. 148)... 

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... 

An account of the mechanism for creep in solids placed under a compressive hydrostatic suess which involves atom-vacancy diffusion only is considered in Nabano and Hemirg s (1950) volume diffusion model. The counter-movement of atoms and vacancies tends to relieve the effects of applied pressure, causing extension normal to the applied sU ess, and sluinkage in the direction of the applied sU ess, as might be anticipated from Le Chatelier s principle. The opposite movement occurs in the case of a tensile sU ess. The analysis yields the relationship... 

Difl erential thermal analysis (DTA) and differential scanning calorimetry (DSC) are the other mainline thermal techniques. These are methods to identify temperatures at which specific heat changes suddenly or a latent heat is evolved or absorbed by the specimen. DTA is an early technique, invented by Le Chatelier in France in 1887 and improved at the turn of the century by Roberts-Austen (Section 4.2.2). A... 

Both LFL and UFL valnes for mixtnres can be estimated by nse of the Le Chatelier eqnation (Growl and Lonvar 1990). However, the methods have some limitations with respect to calcnlating the UFL for certain mixtnres. Britton (1996) determined that the eqnation does not apply to the UFL of mixtnres containing decomposable components snch as ethylene oxide or to mixtnres containing ethyl ether. Mashnga and Growl (2000) discnss the derivation of Le Chatelier s mixing rnle for flammable limits. 

This example shows how to calculate the LFL and UFL of gas-vapor mixtures, using the Le Chatelier rule (Crowl and Louvar 1990). 

This example illustrates how to calculate the MESG for a gas-vapor mixture using the original Le Chatelier rule, which includes only the MESG values of the combustible components, and the modified Le Chatelier rule (proposed in NFPA 497), which includes inert gases as well. 

Calculate the MESG of the following mixture using hoth the original and the modified Le Chatelier rule ... 

Using the original Le Chatelier rule the mixture MESG will he calculated using only the comhustihle gases (i.e., ignoring the nitrogen). 

It can thus he seen that using the original Le Chatelier rule may result in specilying a flame arrester with smaller apertures. Using the original Le Chatelier rule for flame arresters may he the more the appropriate thing to do (see Section 5.3.1). 

Le Chatelier s Rule allows the calculation of the lower flammability (explosibility) limits for flammable mixtures ... 

According to Le Chatelier s principle, conversion is increased by increasing the temperature and decreasing the pressure. Figure 6-3 shows the effect of temperature on the dehydrogenation of different light paraffins. ... 

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