LeChatelier shift

The slight difference in the average rotational energy of the two forms enhances the heat capacity due to the LeChatelier shift in the equilibrium position as the temperature is changed. This effect is exhibited in the curve for ot labeled e-H2. Equilibrium-hydrogen, e-H2, is hydrogen that is kept in the presence of a catalyst to ensure that the equilibrium between 0-H2 and P-H2 is established at all temperatures. The curve for e-H2 is typical of the heat capacity of a reactive mixture maintained in equilibrium as the temperature is changed. 

LeChatelier s principle states that if a system at equilibrium is subjected to a stress, the equilibrium will shift in a direction that will relieve the stress. One such stress is a change of concentration. In this activity, you will see how changing the concentration of a reactant or product creates a new equilibrium. 

Does this agree with LeChatelier s Principle that for an exothermic reaction the system will shift to form more reactants at higher temperatures Yes, it does. Recall, that that only temperature will affect the value of the equilibrium constant. More reactants are formed because the value of the equilibrium constant decreased when the temperature increased. 

To make MnS(s) more soluble, the above equilibrium must be shifted to the right. Applying LeChatelier s Principle, any process which will reduce either [Mn2+] or [S2 ] will do this. In the presence of 0.10 M HC1 (a strong acid), competing equilibria will lower [S2 ] by producing the weak acids, HS and H2S ... 

Such hydrophobic H-bonding naturally leads to an appreciable reduction in volume, and is therefore increasingly favored at higher pressures. Similarly, in the spirit of LeChatelier s principle, one may expect that the presence of a hydrophobic solute promotes formation of cage structures, i.e., tends to shift the cluster... 

From LeChatelier s principle, higher pressures (higher densities) should shift these equilibria to the right, higher temperatures to the left. Since ruby treats carbon as a condensed phase (and thus of unit activity), its amount does not materially affect the equilibria and, so long as at least some solid carbon appears, the ratios (CO2/CO) and (H D/Ha) are rough measures of the equilibrium positions, ruby s predictions of these ratios for some typical explosives are given in Table IV. 

This analysis shows that a compressive load decreases the molar free energy— and that a positive <5e yrt reduces the magnitude of the decrease for the martensite phase thereby resulting in an increased transformation temperature, consistent with Fig. 24.16. Further analysis shows that the observed shift in transformation temperature results from differences in the Young s moduli of the two phases (see Exercise 24.5). This result is consistent with LeChatelier s principle. 

Equation (3.5-18) has been written in terms of molar heat capacities Cpm(i), rather than heat capacities of formation, because the heat capacities of the elements are on both sides and cancel. The second term of this equation is always positive because the weighted average of the squares is always greater than the square of the average. Equation 3.5-18 is in accord with LeChatelier s principle As the temperature is raised, the equilibrium shifts in the direction that causes the absorption of heat. Equation 3.5-18 can also be derived using CP = — T(d2G/dT2)P (equation 2.5-25). 

When the conditions that affect the rate of a chemical reaction are changed in a system at equilibrium, the rates of the forward and the reverse reaction may be affected differently. If these rates become different, more reactants or products are produced. The direction of the shift of an equilibrium can be predicted qualitatively using LeChatelier s principle. LeChatelier s principle states that if a stress is applied to a system at equilibrium, the equilibrium will tend to shift in a direction to relieve that stress. 

An acidic buffer solution has an excess of all the reactants and products, except for H30. Thus, when we try to change the concentration of H30 by adding strong acid or base, the equilibrium shifts, in accordance with LeChatelier s principle, to resist that change. The pH changes very little. (We will do calculations to show quantitatively how little the pH changes in such systems later in this section.)... 

The equilibrium of a weak base and water has OH as a product. If strong acid is added to the system, the strong acid reacts with the OH. However, more OH is produced as the equilibrium shifts in accordance with LeChatelier s principle, so the pH does not change much. If a strong base is added to the system, the equihbrium shifts to use up some of the added OH, and again, the pH is fairly stable. ... 

LeChatelier s principle (18.3) When a stress is applied to a system at equilibrium, the equilibrium shifts so as to tend to reduce the stress. 

Identify or explain each of the following terms (a) equihbrium, (b) rate of reaction, (c) catalyst, (d) completion, (e) LeChatelier s principle, (/) stress, (g) shift, (h) shift to the right or left, (/) equilibrium constant, and (J) equihbrium constant expression. 

When nitric acid is added to water, large numbers of H3O+ ions are produced. The large increase in [H3O+] shifts the water equilibrium far to the left (LeChatelier s Principle), and the [OR-] decreases. 

Consider an arbitrary mixture of these components at equilibrium, and assume that we inject more hydrogen gas into the container. Because the H2 concentration now exceeds its new equilibrium value, the system is no longer in its equilibrium state, so a net reaction now ensues as the system moves to the new state. The LeChatelier principle states that the net reaction will be in a direction that tends to reduce the effect of the added H2. This can occur if some of the H2 is consumed by reacting with I2 to form more HI in other words, a net reaction occurs in the reverse direction. Chemists usually simply say that the equilibrium shifts to the left . 

Virtually all chemical reactions are accompanied by the liberation or uptake of heat. If we regard heat as a reactant or product in an endothermic or exothermic reaction respectively, we can use the LeChatelier principle to predict the direction in which an increase or decrease in temperature will shift the equilibrium state. Thus for the oxidation of nitrogen, an endothermic process, we can write... 

Suppose this reaction is at equilibrium at some temperature T1 and we raise the temperature to T%. The LeChatelier principle tells us that a net reaction will occur in the direction that will partially counteract this change, meaning that the system must absorb some of this additional heat, and the equilibrium will shift to the right. 

In the section that introduced the LeChatelier principle, it was mentioned that diluting a weak acid such as acetic acid CH3COOH ( HAc ) will shift the dissociation equilibrium to the right ... 

What would LeChatelier s principle predict about adding 0.200 M NH4CI to the solution of Example 11 This salt is composed of ammonium ions and chloride ions. The ammonium ions ought to shift the equilibrium of the ammonia ionization to the left, decreasing the hydroxide ion concentration. 

The buffer solution maintains a relatively constant pH by shifting according to LeChatelier s principle ... 

A buffer solution functions in accordance with LeChatelier s principle, which states that an equilibrium system, when stressed, will shift its equilibrium to relieve that stress. This principle is illustrated by the following examples. 

When strong bases are added to a carboxylic acid, neutralization occurs. The acid protons are removed by the OH to form water and the carboxylate ion. The equilibrium shown in the reaction above is shifted to the right, owing to removal of H+. This is an illustration of LeChatelier s principle. 

These observations and others on the direction of the shift in equilibrium in response to a given change are usually summarized by a statement referred to as the Principle of LeChatelier and Braun (but also known as the Principle of Moderation or the Principle of Spite ) ... 

We may state the principle of LeChatelier in the following way. If the external constraints under which an equilibrium is established are changed, the equilibrium will shift in such a way as to moderate the effect of the change. 

How could the industrial chemist apply LeChatelier s principle to increase her yield of methane She will need to adjust any factors that will shift the equilibrium to the product side of the reaction. 

Thinking it Through Considering LeChatelier s principle first, we see from the chemical equation that three moles of gas (2 mol SO2 plus 1 mol of O2) react to produce two moles of product. The equilibrium will shift to minimize the effect of the change, producing more SO3. Choices (B) and (C) are therefore eliminated from consideration. 

As the pressure is inereased, LeChatelier s principle tells us that the system will shift to reduce the pressure. The system will shift to the side of the equation with fewer moles of gas to reduce the pressure. As the mole fractions calcnlated show, the system shifted to increase the amount of N2O4 and decrease the amonnt of NO2. There are now fewer moles of gas in the system. You can check your work by calculating the new partial pressnres of NO2 and N2O4, and then snbstitute the values into the Kp expression to solve for Kp. If the problem is solved correctly, yon will obtain the Kp value calculated in part (b). 

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