Disruption of Equilibrium

Chemical systems at equilibrium are actually somewhat rare outside the laboratory. For example, the concentrations of reactants and products of the reactions taking place in your body are constandy changing, leading to changes in the forward and reverse reaction rates. These constant fluctuations prevent the reactions from ever reaching equilibrium. In most industrial procedures, the products of reversible reactions are purposely removed as they form, preventing the reverse rate of the reaction from ever rising to match the rate of the forward reaction. 

In general, equilibrium systems are easily disrupted. Every time you take a bottle of vinegar from a cool pantry and hold it in your warm hand, you increase the temperature of the solution and disrupt the equilibrium between acetic acid and its ions. To illustrate the conditions that lead to disruption of equilibria and to show why they do so, let s return to our example of making hydrogen gas from carbon monoxide and water vapor. 

Objective 30 To reiterate, the addition of water vapor to our equilibrium system causes Rateforward 

Increased concentration of reactant for a system at equilibrium with Rateforward = Rate,  

Change in the Rates of Reaction when a Reactant is Added to an Equilibrium System for the Reversible Reaction CO(g) + H20(g) C02(gf) + H2(gf) 

---

The previous section showed that if the decay chain remains undisturbed for a period of approximately 6 times the longest half-lived intermediate nuclide then the chain will be in a state of secular equilibrium (i.e., equal activities for all the nuclides). The key to the utility of the U-series is that several natural processes are capable of disrupting this state of equilibrium. 

Measurement of the equilibrium properties near the LST is difficult because long relaxation times make it impossible to reach equilibrium flow conditions without disruption of the network structure. The fact that some of those properties diverge (e.g. zero-shear viscosity or equilibrium compliance) or equal zero (equilibrium modulus) complicates their determination even more. More promising are time-cure superposition techniques [15] which determine the exponents from the entire relaxation spectrum and not only from the diverging longest mode. 

At low cM, the rate-determining step is the second-order rate of activation by collision, since there is sufficient time between collisions that virtually every activated molecule reacts only the rate constant K appears in the rate law (equation 6.4-22). At high cM, the rate-determining step is the first-order disruption of A molecules, since both activation and deactivation are relatively rapid and at virtual equilibrium. Hence, we have the additional concept of a rapidly established equilibrium in which an elementary process and its reverse are assumed to be at equilibrium, enabling the introduction of an equilibrium constant to replace the ratio of two rate constants. 

We disrupted the equilibrium in the bottle when we allowed out much of the CO2 gas that formerly resided within the space above the liquid conversely, the CO2 dissolved in the liquid remains in solution. 

Suppose we add a solution of Na2S04 to this equilibrium system. The additional sulfate ion will disrupt the equilibrium by Le Chatclier s principle and shift it to the left. This decreases the solubility. The same would be true if you tried to dissolve PbS04 in a solution of Na2S04 instead of pure water—the solubility would be less. This application of Le Chatelier s principle to equilibrium systems of a slightly soluble salt is the common-ion effect. 

HATs catalyze the post-translational acetylation of amino-terminal lysine tails of core histones, which results in disruption of the repressive chromatin folding and an increased DNA accessibility to regulatory proteins. The level of histone acetylation is highly controlled and balanced by the activity of histone deacetylases (HDACs), the opponents of HATs. Generally, acetylation is correlated with activation and deacetylation with repression of gene expression. Therefore, the dynamic equilibrium of these proteins represents a key mechanism of gene regulation. 

Macromolecular crystals grow in an equilibrium state with their mother liquor. Disrupting this equilibrium can often destroy the crystals or their ability to diffract X-rays. This situation can be exacerbated by the transfer of the crystal to a solution containing a heavy atom. Therefore, it is important, once crystals are removed from their sealed environment, to first transfer them to a stabilizing solution and let them re-equilibrate before further transfer to the heavy atom solution. Usually, a stabilizing solution is identical to the mother liquor in which the crystal was grown, but with a higher concentration of precipitant. 

Fig. 3. The oncogenic shock model. Tumor cells exhibit an equilibrium between pro-survival and pro-apoptotic signals, such that pro-survival predominates. Upon disruption of the oncogenic driving-force, the pro-survival signals dissipate at a more rapid rate than the pro-apoptotic signals, such that there is a period during which pro-apoptotis predominates. Thus, tumor cells undergo tumor cell death.

If the radio-frequency power is too high, relaxation cannot compete with the disruption of the equilibrium of spins. The population difference between the nuclear magnetic... 

---