Calcium carbonate, dissociation

For a reaction with positive gas mole change, Eq. (47) indicates that Kx decreases with pressure. Because ce is a monotonically increasing function of Kx, the equilibrium extent of a reaction with positive Avgas always decreases as pressure is increased. This is an example of Le Chatelier s principle, which states that a reaction at equilibrium shifts in response to a change in external conditions in a way that moderates the change. In this case, because the reaction increases the number of moles of gas and thus the pressure, the reaction shifts back to reactants. The isothermal compressibility of a reactive system can, therefore, be much greater than that of a nonreactive system. This effect can be dramatic in systems with condensed phases. For example, in the calcium carbonate dissociation discussed in Example 12, if the external pressure is raised above the dissociation pressure of C02, the system will compress down to the volume of the solid. Of course, a similar effect is observed in simple vaporization or sublimation equilibrium. As the pressure on water at 100°C is increased above 1.0 atm, all vapor is removed from the system. 

Exercise 3,8,4, Calcium carbonate dissociates into calcium oxide and carbon... 

First Carbonation. The process stream OH is raised to 3.0 with carbon dioxide. Juice is recycled either internally or in a separate vessel to provide seed for calcium carbonate growth. Retention time is 15—20 min at 80—85°C. OH of the juice purification process streams is more descriptive than pH for two reasons first, all of the important solution chemistry depends on reactions of the hydroxyl ion rather than of the hydrogen ion and second, the nature of the C0 2 U20-Ca " equiUbria results in a OH which is independent of the temperature of the solution. AH of the temperature effects on the dissociation constant of water are reflected by the pH. 

Provided that the temperature and the carbon dioxide pressure conditions in the calcination furnace are such that they correspond to the point A, or to any point above the calcium carbonate line, no dissociation occurs because in such a situation,... 

The insolubility of calcium carbonate is clearly evident from the value of the solubility product, Ksp, in water at 25°C Ksp = 8.7 x 10-9. The carbonate ions are produced in seawater by the dissociation of carbonic acid that forms from the... 

First the aqueous C02 dissociates in water, producing carbonic acid, then the acid attacks the anorthite, leaching Ca2+ and neutralizing the acid, and finally, calcium carbonate precipitates. 

Like chalk, limestone is largely calcium carbonate and dissociates reversibly to lime and carbon dioxide at sufficiently high temperatures (calcination) ... 

Dissolution of Sparingly Soluble Salts. Obtain precipitates of calcium carbonate and calcium oxalate in test tubes by reacting the relevant salts. Decant the solutions and pour an acetic acid solution onto the moist precipitates. What happens Repeat the experiment, but use hydrochloric acid instead of the acetic acid. Write the equations of the chemical reactions in the molecular and net ionic forms. Explain the results obtained on the basis of the dissociation constants of the acids and the solubility product. 

C104 (not HCIO4). insoluble salts and weak electrolytes are not written in ionic form, even though a minor fraction of each ion may actually exist in solution. For example, we indicate the formula for calcium carbonate as CaC03 (not Ca2+ + CO ). Similarly, for slightly dissociated acetic acid, we use the molecular formula HC2H302 instead flf H+ + C2H302. 

When calcium carbonate is heated strongly it thermally dissociates (breaks up reversibly) to form calcium oxide (lime) and carbon dioxide. 

After sterilization, yeast is added to initiate fermentation. McConnell and Schramm (1995) recommend inoculation with no less than 10% by volume. Moreover, as the pH of honey is naturally low and because it is poorly buffered, the pH of must may drop during fermentation to a point limiting yeast efficiency. pH reduction can result from the synthesis of acetic and succinic acids by the yeast cells (Sroka and Tuszynski, 2007). While a rapid decline in pH inhibits undesirable microbial activity (Sroka and Tuszynski, 2007), it also reduces the dissociation of fatty acids in the wort, potentially slowing yeast metabolic action. For this, addition of a buffer is important to maintain the pH within a range of 3.7-4.0 throughout fermentation (McConnell and Schramm, 1995). Calcium carbonate, potassium carbonate, potassium bicarbonate, and tartaric acid are potential candidates. However, as some of these salts can add a bitter-salty... 

In the dissociation of calcium carbonate there will be three phases, viz., two solid phases (CaC03 and CaO) and one gaseous phase (C02). 

Dissociation of calcium carbonate The case of dissociation of calcium carbonate is rather complicated. Its equilibrium can be represented as ... 

Thermal stability. The degree to which a compound resists dissociation or other chemical alteration at elevated temperatures. Magnesium oxide is stable up to its melting point (2800° C.) and beyond, and hence is considered to have high thermal stability calcium bicarbonate decomposes at 100° to carbon dioxide, water, and calcium carbonate, and hence is thermally unstable. As used in the text, the term indicates chemical integrity up to a designated temperature. 

Carbonate alkalinity is not a directly analyzable quantity, but it can be derived from the titration alkalinity (A ) by a relationship which is temperature and pressure dependent. pH is also variable with pressure and temperature. In addition, pH can be defined several ways depending on which buffer system is used, whether liquid junction potentials are considered, and what definition of ionic strength is used. The values of the apparent dissociation constants and calcium carbonate solubility constants are dependent on exactly what definition of seawater pH is used and what standardization technique is used (15, 16, 17). 

The deduction of the formula on the assumption of a constant value of i is only allowable for the limiting case of extreme dilution with accompanying complete dissociation then i = 3 for acid calcium carbonate, which breaks up into the ions Ca and 2, (CO3H). Hence A = cPo 333,... 

Dissociation of calcium carbonate. Tension of dissociation.—Guided by the intuitions of H. Sainte-Claire Deville, H. Debray has proved that the laws of the vaporization of a liquid, laws which we have just recaUed, may be applied almost literally to the chemical decomposition of certain bodies, notably to the dissociation of carbonate of calcium into lime and carbonic acid gas. 

The decomposition of calcium carbonate is not the only reaction showing a dissociation tension, fixed at each temperature and similar in all points to the tension of saturated vapors H. Debray found the same law in studying the decomposition of a certain number of hydrated salts into water vapor and anhydrides. 

A tem containing calcium carbonate, lime, and carbonic acid gas consists of two independent components (o 2) divided into three phases =S) it is a monovariant i stem at a givax temperature the i stem is in equilibrium for a definite value of the pressure, called Ihe dissociation tension of calcium carbonate at the given temperature this tension depends exclusively upon the temperature it depends in no wise upon the masses of the independent components, lime, and carbonic anhydride, which make up the intern this is the celebrated law predicted by Henri Sainte-Claire Deville, demonstrated by Debray for the case that we have just taken as example, and confirmed by Debray and by G. Wiedemann vdien studying the dissociation of hydrated salts, and by Isambert from a study of the dissociation of compounds that ammonia gas forms with certain metallic chlorides. 

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