Enthalpy of Formation: Calcium vs. Magnesium Carbonate

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Discussion Overview

The discussion revolves around the enthalpy of formation of calcium carbonate (CaCO3) compared to magnesium carbonate (MgCO3). Participants explore the relationship between enthalpy of formation, lattice energy, bond strength, and electronegativity, while seeking to understand the factors influencing these values.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that the larger radius of calcium compared to magnesium may result in lower lattice energy for CaCO3 than for MgCO3.
  • Another participant provides specific enthalpy values for both compounds at 298K but expresses uncertainty about the decisive factors influencing these values.
  • A participant proposes that enthalpy of formation is related to bond strength and atomic attraction, but seeks clarification on the concept of lattice energy.
  • Electronegativity is introduced as a potential factor, with one participant noting that magnesium has a higher electronegativity than calcium.
  • There is a discussion about the independence of heat of formation from electronegativity, with participants questioning how these concepts interrelate.
  • Several participants seek a formal definition of electronegativity and its implications for enthalpy of formation.
  • A participant expresses skepticism about the lack of connection between heat of formation and electronegativity, suggesting that other factors may also play a role.
  • One participant shifts the topic to inquire about standard enthalpy and entropy values for other compounds, indicating a broader interest in thermodynamic properties.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the relationship between enthalpy of formation, lattice energy, and electronegativity. Multiple competing views and uncertainties remain regarding the decisive factors influencing the enthalpy of formation for calcium and magnesium carbonates.

Contextual Notes

Participants express uncertainty about the definitions and relationships between key concepts such as lattice energy and electronegativity, indicating a need for further clarification. The discussion also highlights the complexity of thermodynamic properties and their interdependencies.

Harmony
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Question Statement:
Would you expect the enthalpy change of formation of calcium carbonate to be higher or lower than that of magnesium carbonate.

What I think:
Calcium has a bigger radius than magnesium, hence I expect the lattice energy of MgCO3 to be greater than the CaCO3.

I suspect that the enthalpy of formation is related to the lattice energy. But as for how I am not sure. Can anyone enlighten me on this question?
 
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I checked in my files the enthalpy at 298K:

H°(CaCO3) = -1207126 J/mol
H°(MgCO3) = -1095797 J/mol

You can get other info there:

http://webmineral.com/data/Dolomite.shtml
http://webmineral.com/data/Calcite.shtml

I cannot really answer the question. I don't know what is the decisive aspect.
Your answer is not clear for me. The lattice of the dolomite is shorter indeed, but Mg and Ca also have differences in their lattice: atomic density but also the crystallography.
 
Last edited:
i think the enthalpy of formation is related to bond strength and attraction between atoms in the formation. but i still don't know what u mean exactly by lattice energy
 
How might electronegativity be used to explain this. Magnesium has a higher electronegativity than calcium.

Element Electronegativity (pauling scale)

Ca 1.00
Mg 1.31
 
yep...well than it has something to do with internal energy of the elements, but how can the heat of formation be indpendant of electronegativity ?
 
what is the exact definition of electronegativity ?
 
thirst for negative charge
 
Yes:

FunkyDwarf said:
thirst for negative charge

we all know that.

But a more formal definition may help. There is maybe a link with the enthalpy of formation ...
 
Electronegativity is the pull that a certain atom has to attract another atom...i think u can get a better definition from Wikipedia
i would really be surprised if the heat of formation had nothing to do with electronegativity, but there mayb another factor, there should be another factor actually
 
  • #10
I want to know the standard enthalpy and entropy values for the following:

TiN (Titanium Nitride)
TiC (Titanium Carbide)
VC (Vanadium Carbide)
VN (Vanadium Nitride)
 

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