Le Chatelier’s principle

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 ... 

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... 

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)... 

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... 

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. ... 

Click Chemistry Interactive for the self-study module Le Chatelier s principle a water tank analogy. 

According to Le Chatelier s principle, if a chemical system at equilibrium is disturbed by adding a gaseous species (reactant or product), the reaction will proceed in such a direction as to consume part of the added species. Conversely, if a gaseous species is removed, die... 

Reality Check Note that the equilibrium partial pressure of HI is intermediate between its value before equilibrium was established (0.80 atm) and that immediately afterward (1.00 atm). This is exactly what Le Chatelier s principle predicts part of the added HI is consumed to re-establish equilibrium. 

Le Chatelier s principle A relation stating that when a system at equilibrium is disturbed it responds in such a way as to partially counteract that change, 337-338 buffers and, 385 compression effects, 339-340 expansion effects, 339-340 precipitation equilibrium, 442 reaction conditions, 348q temperature changes, 340 Lead, 2,501 Leclanch cell, 500 Leucine, 622t... 

We are not satisfied with the conclusion that this change or that change affects the equilibrium concentrations. We would also like to predict the direction of the effect (does it favor products or reactants ) and the magnitude of the effect (how much does it favor products or reactants ). The first desire, to know the qualitative effects, is answered by a generalization first proposed by a French chemist, Henry Louis Le Chatelier, and now called Le Chatelier s Principle. 

A new state of equilibrium is then attained in which more FeSCN+2 is present than was there before the addition of SCN-. Increasing the concentration of SCN- has increased the concentration of the FeSCN+2 ion. This is in accord with Le Chatelier s Principle. The change imposed on the system was an increase in the concentration of SCN-. This change can be counteracted in part by some Fe+3 and SCN- ions reacting to form more FeSCN+2. The same argument applies to an addition of ferric ion from a soluble ferric salt. In each case, the formation of FeSCN+s uses up a portion of the added reactant, partially counteracting the change. 

Does Le Chatelier s Principle predict a change of equilibrium concentrations for the following reactions if the gas mixture is compressed If so, does the change favor reactants or products ... 

Our experimental observations indicated that warming a bulb containing N02 and N204 caused a shift of the equilibrium state in favor of the formation of N02 (the reddish-brown color deepened). It is easy to see that this is in accord with Le Chatelier s Principle. A rise in temperature is caused by an input of heat. At the higher... 

Raising the temperature of liquid water raises its vapor pressure. This is in accord with Le Chatelier s Principle since heat is absorbed as the liquid vaporizes. This absorption of heat, which accompanies the change to the new equilibrium conditions, partially counteracts the temperature rise which caused the change. 

Knowledge of chemical principles pays rewards in technological progress. Control of chemical reactions is the key. The large scale commercial production of nitrogen compounds provides a practical example of the beneficial application of Le Chatelier s Principle. 

Can we predict the optimum conditions for a high yield of NH3 Should the system be allowed to attain equilibrium at a low or a high temperature Application of Le Chatelier s Principle suggests that the lower the temperature the more the equilibrium state will favor the production of NHS. Should we use a low or a high pressure The production of NH3 represents a decrease in total moles present from 4 to 2. Again Le Chatelier s Principle suggests use of pressure to increase concentration. But what about practicality At low temperatures reaction rates are slow. Therefore a compromise is necessary. Low temperature is required for a desirable equilibrium state and high temperature is necessary for a satisfactory rate. The compromise used industrially involves an intermediate temperature around 500°C and even then the success of the... 

Le Chatelier s Principle permits the chemist to make qualitative predictions about the equilibrium state. Despite the usefulness of such predictions, they represent far less than we wish to know. It is a help to know that raising the pressure will favor production of NH3 in reaction (10a). But how much will the pressure change favor NH3 production Will the yield change by a factor of ten or by one-tenth of a percent To control a reaction, we need quantitative information about equilibrium. Experiments show that quantitative predictions are possible and they can be explained in terms of our view of equilibrium on the molecular level. 

This heat effect can be used in predicting how K changes with temperature. Le Chatelier s Principle indi-... 

This is in accord with Le Chatelier s Principle. Addition of HC1 to water raises [H+]. By Le Chatelier s Principle, processes take place that tend to counteract partially the imposed change. Reaction with OH (aq) does tend to counteract the raised concentration of H+(aq). 

Again Le Chatelier s Principle tells us qualitatively what will occur and the equilibrium expression tells us quantitatively. If we add OH-(ag), a change will take place that tends to counteract partially the resulting increase in [OH-]. This occurs through the reaction between OY (aq) and H+(aq), consuming both ions and reducing the value of [H+] X [OH-]. Reaction continues until this product reaches the equilibrium value, K = 1.00 X 10-14. 

Le Chatelier s Principle, the removal of Zn+2 tends to shift equilibrium toward the products. Therefore, removing Zn+2 increases the tendency for reaction (63) to occur. Our prediction of reaction is still valid. 

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