Le Chdtelier s Principle

Henry-Louis Le Chdtelier was a French chemist. He devised Le Chdtelier s principle, which explains the effect of a change in conditions on a chemical equilibrium. He also worked on the variation in the solubility of salts in an ideal solution. 

Le Chdtelier s principle tells us that adding electrons to the right side of Reaction 21-6 drives the reaction back to the left. 

Now all spontaneous fluxes Jm of a given sign naturally bring about a change of opposite sign in their associated, conjugate forces [i.e., in 6Xp in this case see also Exercise 6.4.1]. This, in combination with the result just cited, means that Jm cannot be sustained the system ultimately returns to the initial, quiescent, stationary state. We thus deal here with an extension of Le Chdtelier s principle to steady-state... 

Pressure affects gases in a system much more than it affects liquid or solids. We will investigate the same ammonia, hydrogen, nitrogen system discussed before. If the system is at equilibrium, what will an increase in pressure by the chemist do to the equilibrium The system will shift to try to reduce the stress, as required by Le Chdtelier s principle. How can this system reduce its own pressure By reducing the total number of moles present. It can shift to the right to produce 2 mol of gas for every 4 mol used up ... 

Research the practical uses of Le Chdtelier s principle. Present your results to your class. 

Use the following terms to create a concept map chemical equilibrium, equilibrium constant, solubility product constant, reversible reactions, and Le Chdtelier s principle. 

If a base is added to the buffer solution, the base will react with the H30" and remove some of this ion from solution. According to Le Chdtelier s principle, the equilibrium will adjust by shifting to the right to make more H30, preventing too great a pH change. It is a similar story if an acid is added. The tendency for [HsO" ] to increase is countered by a shift of the equilibrium to the left and the formation of more HX molecules. 

Pressure. Pressure, like temperature, can affect the rate of reaction as well as the equilibrium position. The rate of reaction is generally increased by increasing pressure, because a gas phase is usually present, and increased pressure gives increased concentration. In general, increased concentration speeds up a reaction. Pressure increases the equilibrium yield in a hydrogenation reaction when there is a decrease in the volume of the reaction as it proceeds. This is the simple application of the mass-action law, or Le Chdtelier s principle. In hydrogenation reactions, there is usuaUy a decrease in volume. 

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

Le Chdtelier s principle predcts that the forward, endothermic reaction is favored by heating. 

These statements express the application to temperature and pressure changes of what is known as Le Chdtelier s principle When a change is made to a closed system at equilibrium, the equilibrium shifts in the direction that tends to oppose the change. Here are two examples. 

According to Le Chdtelier s principle, a system at equilibrium will react to stress by shifting in the direction that will partially offset the effect of the stress. 

According to Le Chdtelier s principle, when stress is applied to a reaction at equilibrium, the equilibrium will shift to relieve that stress. 

Steady-state conditions tend to be inherently stable consider a case where all forces except one, namely X, k + I 0, Lmm > 0. Thus, Jm Xm > 0. Now, any flow of a given magnitude brings about a change of opposite sign in the associated conjugate force this matter is explored in the Comments section. Therefore, the flow Jm cannot be sustained the system ultimately returns to the quiescent condition. We see that this leads to an application of Le Chdtelier s principle to steady-state phenomena. Steady-state conditions remain stationary. 

Le Chdtelier s principle states that when a stress is applied to a system at equilibrium, the system will respond by shifting in the direction that minimizes the effect of the stress. In this context, stress refers to a disturbance of the system at equihbrimn by any of the following means ... 

Increasing [PH ], as would be the case in making the solution basic, means decreasing [H ]. In fact, PH = 1M corresponds to [H" ] = 1 x 10 M. Because equation (22.53) has H (aq) on the left side of the equation, a decrease in [H ] favors the reverse reaction (by Le Chdtelier s principle). At some point before the solution becomes basic, the forward reaction is no longer spontaneous. 

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