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I’m studying some chemical engineering process and my teacher made a question in class that nobody knew how to answer it and then she asked to made a search after class. However, I don’t even found nothing related.

$$\ce{2 NaCl + CaCO3 -> Na2CO3 + CaCl2 (do not occur spontaneously)}$$

Do you know why $\ce{NaCl + CaCO3}$ reaction do not occur in a spontaneous form in a process? I know that in Solvay Process we need to produce $\ce{CO2}$ from $\ce{CaCO3}$ from heating, but I really don’t know why we couldn’t do this reaction right away.

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Calcium Carbonate $\ce{CaCO3}$ is almost insoluble

Here a little digging is required as $\ce{NaCl + CaCO3 -> Na2CO3 + CaCl2}$ of the Solvay Process leaves out a few steps.

The primary driver of the process is that sodium bicarbonate is less soluble in $\ce{NaCl}$ brine than $\ce{NH4Cl}$, and the starting materials are very inexpensive salt brine and limestone. The product is widely used "soda ash" $\ce{Na2CO3}$.

The more detailed steps are as follows:

$$\ce{CaCO3 ->[\Delta] CaO (s) + CO2(g)}$$

$$\ce{NaCl(brine) + NH3 + CO2 -> NaHCO3 \downarrow + NH4Cl (aq)}$$

Ammonia is recovered using highly basic $\ce{CaO}$ as:

$$\ce{2NH4Cl + CaO -> 2 NH3(g) + CaCl2 + H2O}$$

Bicarbonate is calcined to soda ash as:

$$\ce{2 NaHCO3 ->[\Delta] Na2CO3 (s) + CO2 + H2O}$$

Ammonia and $\ce{CO2}$ are thus recovered and recycled. By product $\ce{CaCl2}$ is road salt.

Production and isolation of desired products by phase change is highlighted in these reactions: $\ce{limestone -> CaO + CO2 (reactant)}$, $\ce{NaHCO3}$ by precipitation, recovery of ammonia gas, and conversion of bicarbonate to solid soda ash by removing $\ce{CO2}$ and $\ce{H2O}$ as gasses.

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The proposed reaction $\ce{2NaCl + CaCO3 -> Na2CO3 + CaCl2}$ does not occur, and cannot occur by simple mixing in solution. On the contrary the reaction will be reversed, because $\ce{CaCO3}$ is the only insoluble product in the reaction. Let me explain the reason why.

If you mix two solutions, one of $\ce{Na2CO3}$ and one of $\ce{CaCl2}$, both solutions contain ions, namely $\ce{Na^+, CO3^{2-}, Ca^{2+}, Cl^-}$, and nothing can prevent the following reaction to occur :$$\ce{Ca^{2+} + CO3^{2-} -> CaCO3(s)}$$ So the substances formed on the right-hand-side of the proposed equation cannot occur simultaneously in an aqueous solution. If they were present simultaneously in a solution, their ions would interact. $\ce{CaCO3}$ will precipitate and the proposed reaction will occur in the reverse direction $$\ce{Na2CO3 + CaCl2 -> 2 NaCl + CaCO3(s)}$$

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