Decomposition of calcium carbonate

You will notice that AS° for the decomposition of calcium carbonate is a positive quan- ... 

An example of a reaction for which AH° and AS° have the same sign is the decomposition of calcium carbonate ... 

Chen, C.-T.A. (1978). Decomposition of calcium carbonate and organic carbon in the deep oceans. Science 201, 735-736. 

Consideration thus far has been on only balanced reactions which occur in one phase, that is, homogeneous reactions. There are, of course, a great many reactions which occur between substances in different phases, and these are known as heterogeneous reactions. Numerous reversible, heterogeneous reactions are known, and it is pertinent now to bestow consideration on how far the law of mass action can be applied to such cases. The familiar reaction of the decomposition of calcium carbonate thermally - a well-known example of a reversible reaction represented by the equation... 

B (a) Because AngiS = +1 for the decomposition of calcium carbonate, we would predict AS >0 for the reaction, favoring the reaction at high temperatures. High temperatures also favor this endothermic (ATT > 0) reaction. 

Fig. 60. TMBA- and MS-curves of the decomposition of calcium carbonate. Heating rate...

Stage III The decomposition of calcium carbonate to calcium oxide, which is a function of the partial pressure of the C02 in contact with the sample. The endothermal band for the carbonate decomposition is sharply peaked spread over a relatively narrower temperature range in an atmosphere of C02. 

The lime is produced by the thermal decomposition of calcium carbonate in shells dredged up from the ocean floor. The precipitated magnesium hydroxide is filtered off and treated with hydrochloric acid ... 

FIGURE 13.3 Thermal decomposition of calcium carbonate CaC03(s) ... 

PROBLEM 17.6 By determining the sign of AStotai, show whether the decomposition of calcium carbonate is spontaneous under standard-state conditions at 25°C. 

The concept of a reversible chemical reaction may be illustrated by the decomposition of calcium carbonate, which when heated forms calcium oxide and carbon dioxide gas. At equilibrium, this system exerts a definite decomposition pressure of C02 for a given temperature. When the pressure falls below this value, CaCOj decomposes. Assume now that a cylinder is fitted with a frictionless piston and contains CaC03, CaO, and C02 in equilibrium. It is immersed in a constant-temperature bath, as shown in Fig. 2.5, with the temperature adjusted to a value such that the decomposition pressure is just sufficient to balance the weight on the piston. The system is in mechanical equilibrium, the temperature of the system is equal to that of the bath, and the chemical reaction is held in balance by the pressure of the COj. Any change of conditions, however slight,... 

Quicklime (CaO) is produced by the thermal decomposition of calcium carbonate (CaC03). Calculate the volume of C02 produced at STP from the decomposition of 152 g of CaC03 according to the reaction... 

So far, we have discussed equilibria only for systems in the gas phase, where all reactants and products are gases. These situations represent homogeneous equilibria. However, many equilibria involve more than one phase and are called heterogeneous equilibria. For example, the thermal decomposition of calcium carbonate in the commercial preparation of lime occurs by a reaction involving both solid and gas phases ... 

Lime, used here as a fertilizer, is produced in the thermal decomposition of calcium carbonate. 

The first conclusion to be drawn from the application of the fundamental equation is that when only one substance is present as gas or vapour, which is absent in the solid form, its concentration must be constant at any given temperature, i. e. its pressure must be. The phenomenon thus, by the existence of a maximum pressure, connects with that of simple evaporation e. g. there is a maximum pressure for the partial decomposition of calcium carbonate ... 

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. 

Other important examples of two component systems are the heterogeneous dissociation equihbria, in which a chemical compound in one phase forms products of decomposition which belong to a different phase. The standard example of a reaction of this kind is the decomposition of calcium carbonate according to the equation CaC03 = Ca0 + C02. Here we have three com-... 

If the reaction is carried out in a closed vessel, the conversion is not complete, as the partial pressures of the gases formed would attain very large values if any considerable quantity of water vapour, the gases are removed as fast as they are formed, so that their partial pressure at the surface of the carbon is maintained at a small value. In this way only is the complete oonversion of the carbon into water gas possible. Currents of gases are employed in a similar manner in the decomposition of calcium carbonate (the burning of lime) and in the reduction of ores by carbon monoxide. This procedure is used extensively in technical processes. 

The decomposition of calcium carbonate to calcium oxide and carbon dioxide needs a lot of heat energy. 

Reversible reactions. Many solid-gas reactions are reversible, e.g., dehydration of crystal hydrates, so that rate equations for such processes should include terms for the rate of the reverse reaction. If the rates of contributing forward and reverse reactions are comparable, the general set of kinetic models (Table 3.3.) will not be applicable. The decomposition step in a reversible reaction thus needs to be studied [94] under conditions as far removed from equilibrium as possible (e.g. low pressures or high flow rates of carrier gas) and sensitive tests are required for determining whether the kinetics vary with the prevailing conditions. Sinev [95] has calculated that, for the decomposition of calcium carbonate, the rate of the reverse reaction is comparable with that of the forward reaction even when small sample masses (10 mg) and high flow rates (200 cm s ) of inert gas are used. Interpretation of observations becomes more difficult and the reliabihty of conclusions decreases if local inhomogeneities of kinetic behaviour develop within the reactant mass. 

Kinetic data measured for the decomposition of calcium carbonate under isothermal and under programmed-temperature conditions [11] and varied reaction environments influencing the ease of removal of the CO2 product, show that the apparent values of the kinetic parameters k, A and may be influenced by sample heating rate, reactant self-cooling, sample mass, geometry and particle size, which determine the rate because of the reversible nature of the decomposition [12]. These effects can lead to compensation behaviour [13]. 

Figure 1-9 Diagram of the decomposition of calcium carbonate to give a white solid A (56.0% by mass) and a gas B (44.0% by mass). This decomposition into simpler substances at a fixed ratio proves that calcium carbonate is a compound. The white solid A further decomposes to give the elements calcium (71.5% by mass) and oxygen (28.5% by mass). This proves that the white solid A is a compound it is known as calcium oxide. The gas B also can be broken down to give the elements carbon (27.3% by mass) and oxygen (72.7% by mass). This establishes that gas B is a compound it is known as carbon dioxide.

The thermal decomposition of calcium carbonate (limestone) and other carbonates produces two compounds, a metal oxide and carbon dioxide ... 

It is common practice to check the performance of a TGA system by running a sample of calcium oxalate monohydrate. This salt is known to thermally decompose in three stages over well-defined temperature ranges. The first step involves the loss of the single water of hydration molecule followed sequentially by the conversion of anhydrous calcium oxalate to calcium carbonate with the loss of carbon monoxide, and thence the decomposition of calcium carbonate to calcium oxide with the evolution of carbon dioxide. 

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