Le Chatelier’s principle A system

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... 

Le Chatelier s principle a system that in equilibrium is disturbed adjusts so as to minimize the disturbance. 

According to Le Chatelier s principle, a system at equilibrium will react to counteract any disturbance to the equilibrium. Thus, removing a product from a reaction mixture as it is formed drives the equilibrium to the right, forming more product. 

Le Chatelier s principle A system at equilibrium will react to any perturbation so as to resist the change being forced on it. 

A reaction can have a positive AG° and still proceed. For example, if the reaction had an unfavorable equilibrium constant with AG° as +2.72 kcal/mol (+11.39 kJ/mol), the equilibrium mixture would contain a 99 1 R to P mixture. If we started the reaction with 100 mol of pure R, the reaction would be spontaneous and produce 1 mol of P to give the equilibrium mixture. By Le Chatelier s principle, a system at equilibrium will respond to any change by shifting to restore the equilibrium mixture. If a subsequent reaction removed the small amount of P that was formed, then more P would be produced to restore the equilibrium mixture. That following reaction would act as a driving force to overcome an unfavorable R to P 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... 

Now consider what happens if some acid is added to this saturated solution. Hydronium ions react with hydroxide ions to form water OH a q) + H3 O (a 2H2 0(/) By Le Chatelier s principle, the system responds In... 

The left part of the figure shows the attainment of equilibrium starting from the initial conditions of Example 14.10. Then the equilibrium state is abruptly perturbed by an increase in the partial pressure of H2 to 2.000 atm. In accordance with Le Chatelier s principle, the system responds (Example 14.15) in such a way as to decrease the partial pressure of H2—that is, to counteract the perturbation that moved it away from equilibrium in the first place. 

If a system at equilibrium is disturbed by a change in conditions (concentration, pressure, or temperature), it will temporarily be out of equilibrium. However, it will then undergo a net reaction to reach equilibrium again (Le Chatelier s principle). A change in concentration or pressure does not affect K, but a change in temperature does. 

Le Chatelier s principle A principle stating that if a system in a state of equilibrium is disturbed, it will undergo a change that shifts its equilibrium position in a direction that reduces the effect of the disturbance. (561)... 

When the volume of a gas is decreased (when a gas is compressed), the pressure increases. This occurs because the molecules present are now contained in a smaller space and they hit the walls of their container more often, giving a greater pressure. Therefore, when the volume of a gaseous reaction system at equilibrium is suddenly reduced, leading to a sudden increase in pressure, by Le Chatelier s principle the system will shift in the direction that reduces the pressure. 

Strategy A change in pressure can affect only the volume of a gas, but not that of a solid or liquid because solids and liquids are much less compressible. The stress applied is an increase in pressure. According to Le Chatelier s principle, the system will adjust to partially offset this stress. In other words, the system will adjust to decrease the pressure. This can be achieved by shifting to the side of the equation that has fewer moles of gas. Recall that pressure is directly proportional to moles of gas PV = nRT soP xn. 

Le Chatelier s principle A principle stating that when we disturb a system at chemical equihbrium, the relative concentrations of reactants and products shift so as to partially undo the effects of the disturbance. (Section 15.7)... 

Suppose we disturb the equilibrium by adding NO2 to the equilibrium mixture ( Figure 15.9). In other words, we increase the concentration of NO2. What happens According to Le Chatelier s principle, the system shifts in a direction to minimize the disturbance. The shift is caused by the increased concentration of NO2, which in turn increases the rate of the reverse reaction because reaction rates generally increase with increasing concentration (as we discussed in Section 15.2). 

As expressed by Le Chatelier s principle, a stress placed upon a system in equilibrium will shift the equilibrium to relieve the stress. For example, adding product D to a system in equilibrium will cause Reaction 19.15 to shift to the left, consuming C and producing A and B, until the equilibrium constant expression is again satisfied. This mass action effect is the driving force behind many environmental chemical phenomena. 

Le Chatelier s principle A law that states that ifa system in physical or chemical equilibrium is subjected to a change in temperamre, pressure, or concentration, then the system will automatically alter itself so as to reduce the effects of the change. It can be shown that this law must be true if energy is neither created nor destroyed. 

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. 

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)... 

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... 

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. 

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 When a stress is applied to a system in dynamic equilibrium, the equilibrium tends to adjust to minimize the effect of the stress. 

FIGURE 9.13 Le Chatelier s principle predicts that, when a reaction at equilibrium is compressed, the number of molecules in the gas phase will tend to decrease. This diagram illustrates the effect of compression and expansion on the dissociation equilibrium ot a diatomic molecule. Note the increase in the relative concentration of diatomic molecules as the system is compressed and the decrease when the system expands. 

Le Chatelier s principle When a stress is applied to a system in dynamic equilibrium, the equilibrium adjusts to minimize the effect of the stress. Example a reaction at equilibrium tends to proceed in the endothermic direction when the temperature is raised, leveling The observation that strong acids all have the same strength in water, and all behave as though they were solutions of H,Of ions. 

A quick qualitative indication of how a system at equilibrium responds to a change in conditions can be obtained using Le Chatelier s principle, which was first formulated in 1884 by Henri-Louis Le Chatelier, a French industrial chemist. 

Le Chatelier s principle is a compact summary of how different factors influence equilibrium. Introducing a reagent causes a reaction to proceed in the direction that consumes the reagent. Reducing the temperature removes heat from the system and causes the reaction to produce heat by proceeding in the exothermic direction. 

The effects of changes in amounts on a system at equilibrium can be summarized in accordance with Le Chatelier s principle ... 

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