LeChatelier s principle

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... 

Given LeChatelier s Principle (when a stress is placed on a system at equilibrium, the system will adjust itself in such a way as to relieve the stress), it seemed that if... 

Recently Lee et al (Ref 3) re-examined the behavior of PETN under 10 to 50 kbars of external pressure. They also find a reduction in decomposition rate with increasing applied pressure. HMX behaves similarly to PETN. TNT whose explosion products contain a high proportion of solid carbon, as expected from LeChatelier s Principle, shows little pressure effect on its thermal decomposition. Nitro-methane, however, appears to decompose more rapidly under an external pressure of 50 kbars than 10 kbars. This effect is not completely understood but Lee et al suggest that high pressure may favor the formation of the thermally less stable aci form of Nitromethane ... 

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. 

C. A. Snyder and D. C. Snyder, "Simple Soda Bottle Solubility and Equilibria," /. Chem. Educ., Vol. 69,1992,573. Bromocresol green indicator, added to a glass bottle of seltzer water, changes color from yellow to green to blue as carbon dioxide concentration is decreased. Observations are related to temperature and pressure effects on gas solubility, and LeChatelier s principle is applied to the equilibria involved. 

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). 

The reactor can operate with either a liquid-phase reaction or a gas-phase reaction. In both types, temperature is very important. With a gas-phase reaction, the operating pressure is also a critical design variable because the kinetic reaction rates in most gas-phase reactions depend on partial pressures of reactants and products. For example, in ammonia synthesis (N2 + 3H2 O 2NH3), the gas-phase reactor is operated at high pressure because of LeChatelier s principle, namely that reactions with a net decrease in moles should be mn at high pressure. The same principle leads to the conclusion that the steam-methane reforming reaction to form synthesis gas (CH4 + H20 O CO + 3 H2) should be conducted at low pressure. 

The test results with the ultrasonic nozzle were obtained with an estimated steam to copper (S/Cu) ratio of 23 and the humidified Ar was injected co-currently with the CuCl2 solution. Several variables remain to be investigated, i.e. lower S/Cu ratios, counter-current instead of co-current operation, and subatmospheric pressures. LeChatelier s Principle predicts that reducing the pressure in the hydrolysis reactor should reduce the S/Cu ratio. The effect of a reduced pressure was quantified by the results of a sensitivity study using Aspen. Aspen predicts that a S/Cu ratio of 17 is needed for essentially complete conversion at 375°C and atmospheric pressure while a S/Cu ratio of 13 is required at 0.5 bar. The conceptual process design specifies that the hydrolysis reactor be run at 0.25 bar. The pressure drop in the reactor is achieved by adding a low temperature steam ejector after the condenser at the exit of the hydrolysis reactor in the conceptual design. 

FIGURE 7.4 Of the 16 chemistry topics examined (1-16) on the final exam, overall the POGIL students had more correct responses to the same topics than their L-I counterparts. Some topics did not appear on all the POGIL exams. Asterisks indicate topics that were asked every semester and compared to the L-I group. The topics included a solution problem (1), Lewis structures (2), chiral center identification (3), salt dissociation (4), neutralization (5), acid-base equilibrium (6), radioactive half-life (7), isomerism (8), ionic compounds (9), biological condensation/hydrolysis (10), intermolecular forces (11), functional group identification (12), salt formation (13), biomolecule identification (14), LeChatelier s principle (15), and physical/chemical property (16). 

In the previous chapters, it was observed that in a real sense the highest specific impulse was obtained for those propellants which gave the highest heat release per unit mass rate of consumption of propellants. In a more ideal sense, maximum specific impulse is obtained when Tc/fH is maximized. For conditions of correct expansion specific impulse increases with increasing chamber pressure for two reasons first, the pressure ratio across the nozzle increases (ambient kept constant) and second according to LeChatelier s principle there is less dissociation at... 

By application of LeChatelier s principle, one can see that reaction 10.5 is favored at lower pH. The reaction of NH2CI with NOM can be interpreted as chloramine demand exerted by NOM oxidation, and written as follows ... 

Because chemical equilibrium involves rates of reactions, this chapter first investigates the factors that affect the rate of a reaction (Section 18.1). The molecular basis of chemical equilibrium and some of its terminology are then presented in Section 18.2. LeChatelier s principle, discussed in Section 18.3, explains qualitatively how to predict what happens to a system at equilibrium when a change is imposed on the system. Section 18.4 presents the equilibrium constant, which allows us to obtain quantitative results for systems at equilibrium. 

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. 

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