Sciencemadness Discussion Board

do a soluble substance react with an insoluble one in a aqueous solution?

Eli25 - 15-5-2015 at 21:25

For-example consider the reaction below:

CaCl2 + MgCo3 ----> CaCo3 + MgCl2

MgCo3 is insoluble while CaCl2 is soluble. If I have a solution of CaCl2 and add MgCo3 to the solution do they react and give CaCo3 ?

Pumukli - 15-5-2015 at 22:45

It depends on how much insoluble that particular insoluble material is. In your example if the solubility of CaCO3 is smaller than the solubility of MgCO3, then the reaction can work. (At least in theory.)
The expression "insoluble" is a delicate one in chemistry because there are differencies of the "insolubilities" of various so-called insoluble materials. There are solubility data compiled into neat tables one can look up.

I wrote "in theory" because solubility is not the only one deciding factor in such reactions. It is nevertheless the main one but there are other factors as well. For example the particle size of the insoluble materials. Big chunks of MgCO3 has relatively small surface area and if the reaction can work (solubility decides) it still can stop quickly due to the precipitation/crystallization of a thin CaCO3 layer which hinders diffusion. Temperature, stirring the solution or not also has their effect.

phlogiston - 16-5-2015 at 05:11

Sometimes you can drive the reaction forward by removing one of the products.
For example, I have once dissolved barium carbonate in a boiling ammonium nitrate solution to prepare barium nitrate.

Like most 'insoluble' compounds, a minute amount of barium carbonate will dissolve and the reaction is driven to completion because ammonia evolves as a gas. It is an extremely slow process though.

blogfast25 - 16-5-2015 at 05:30

Quote: Originally posted by Eli25  
For-example consider the reaction below:

CaCl2 + MgCo3 ----> CaCo3 + MgCl2

MgCo3 is insoluble while CaCl2 is soluble. If I have a solution of CaCl2 and add MgCo3 to the solution do they react and give CaCo3 ?


It's important to understand that insolubility is very relative and that almost nothing has ABSOLUTE ZERO solubility.

The reaction you chose as example actually takes part in solution:

MgCO3(s) < === > Mg<sup>2+</sup>(aq) + CO<sub>3</sub><sup>2-</sup>(aq) (equilibrium to the left)
CaCl2(s) === > Ca<sup>2+</sup>(aq) + 2 Cl<sup>-</sup>(aq) (equilibrium almost completely to the right)

Thus:

Ca<sup>2+</sup>(aq) + CO<sub>3</sub><sup>2-</sup>(aq) < === > CaCO3(s) (equilibrium almost completely to the right)

Because calcium carbonate is far more insoluble than magnesium carbonate this displacement does proceed.

Whether or not such a reaction actually does proceed or not can be calculated from the equilibrium constants of the 'sub reactions'.

[Edited on 16-5-2015 by blogfast25]

gatosgr - 16-5-2015 at 05:44

From what I remember the entropy of the reaction (Hess's law) says if the reaction is possible energetically or not but the amount of time it takes is determined experimentally. Has anybody of you bothered with how and if there are formulas that relate the kinetics of the reaction with nucleation sites?

[Edited on 16-5-2015 by gatosgr]

blogfast25 - 16-5-2015 at 06:01

Quote: Originally posted by gatosgr  
From what I remember the entropy of the reaction (Hess's law) says if the reaction is possible energetically or not but the amount of time it takes is determined experimentally. Has anybody of you bothered with how and if there are formulas that relate the kinetics of the reaction with nucleation sites?

[Edited on 16-5-2015 by gatosgr]


Actually, it's the change in Gibbs Free Energy ΔG that determines whether reactions are thermodynamically favourable or not.

Thermodynamics says NOTHING about kinetics though.

I'm fairly sure studies of the kind you mentioned [kinetic] have been carried out though.

[Edited on 16-5-2015 by blogfast25]

DraconicAcid - 16-5-2015 at 08:19

The kinetics would depend lot on the particle size, and on the form of the calcium carbonate.

But I know the reaction Ag2CrO4 + 2 Cl- -> 2 AgCl + CrO4= is pretty fast, as it occurs in a Mohr titration.

gatosgr - 16-5-2015 at 08:57

entropy is the same as gibbs energy, enthalpy, helmholtz... just different conditions.. I was interested on metal electroless plating and I know the rate of deposition depends on nucleation sites that reduce the plating metal ions but I don't know how does kinetics depends on it. I see similarities between the entropy of solvation... (I have found some researches that do analysis based on it) meaning the interactions with the solvent particles and the electroaffinity of nucleation sites.. I'm pretty sure someone knows what Im talking about.

[Edited on 16-5-2015 by gatosgr]

blogfast25 - 16-5-2015 at 09:02

Quote: Originally posted by gatosgr  
entropy is the same as gibbs energy, enthalpy, helmholtz... just different conditions..


No, it's not, not strictly speaking anyway.

gatosgr - 16-5-2015 at 09:02

I was interested on metal electroless plating and I know the rate of deposition depends on nucleation sites that reduce the plating metal ions but I don't know how does kinetics depends on it. I see similarities between the entropy of solvation... (I have found some researches that do analysis based on it) meaning the interactions with the solvent particles and the electroaffinity of nucleation sites.. I'm pretty sure someone knows what Im talking about.

blogfast25 - 16-5-2015 at 09:10

Quote: Originally posted by DraconicAcid  
The kinetics would depend lot on the particle size, and on the form of the calcium carbonate.



Studying the kinetics of displacement reactions (of the OP's 'type') may in principle be simpler than one would surmise at first glance.

Assume, rightly I believe, that the dissolution of CaCO3 is the rate limiting step. That rate has to be strongly dependent on surface area, thus particle size, as well as temperature. In that case overall reaction rate would be dependent mainly on CaCO3 granulometry, as well as other characteristics of the CaCO3 that might affect dissolution rates (as well as reaction temperature).

DraconicAcid - 16-5-2015 at 09:14

Quote: Originally posted by gatosgr  
entropy is the same as gibbs energy, enthalpy, helmholtz... just different conditions..


No, it isn't. Not even close....

blogfast25 - 16-5-2015 at 09:19

Quote: Originally posted by DraconicAcid  
No, it isn't. Not even close....


Nah, the difference between Gibbs Free Energy and Entropy is like the difference between energy and power. 'Close 'nuff'. ;)

I mean, it isn't like we're discussing 'science' or somefink like that here, innit?

[Edited on 16-5-2015 by blogfast25]

gatosgr - 16-5-2015 at 11:00

I should say one is derived after another... sorry. They equalize for different conditions.

blogfast25 - 16-5-2015 at 12:32

Quote: Originally posted by gatosgr  
I should say one is derived after another... sorry. They equalize for different conditions.


Explain.

gatosgr - 16-5-2015 at 12:57

Open your textbook mine has these.

DraconicAcid - 16-5-2015 at 12:59

Gibb's Free Energy is derived from entropy and enthalpy, but that does not mean that they are the same thing, or that entropy and enthalpy equalize for different conditions.

gatosgr - 16-5-2015 at 14:11

Well you are missing the context here, the sign of the difference depends on only one of these for different conditions isothermic adiabatic bla bla and this is what determines if the reaction will be possible or not so talking about gibbs or entropy is the same where you refer to the possibility of the reaction I was talking about. But you're right they're not the same as in absolute values or dimensional analysis or meaning..:D

I think that with the maxwell equations they equalize absolutely given the conditions but I'm not in the mood for trying.:D

[Edited on 16-5-2015 by gatosgr]

blogfast25 - 16-5-2015 at 14:24

Quote: Originally posted by gatosgr  
Well you are missing the context here, the sign of the difference depends on only one of these for different conditions isothermic adiabatic bla bla and this is what determines if the reaction will be possible or not so talking about gibbs or entropy is the same where you refer to the possibility of the reaction I was talking about. But you're right they're not the same as in absolute values or dimensional analysis or meaning..:D

I think that with the maxwell equations they equalize absolutely given the conditions.



[Edited on 16-5-2015 by gatosgr]


Gobbledigook. Believe what you want.

I'm done with this.

gatosgr - 16-5-2015 at 14:33

I had to google gobblelkdjfalfeifajld or whatever that was. :D


[Edited on 16-5-2015 by gatosgr]