Enthalpy of Formation

  • Thread starter Harmony
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  • #1
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?
 

Answers and Replies

  • #2
lalbatros
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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:
  • #3
eaboujaoudeh
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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
 
  • #4
chemisttree
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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
 
  • #5
eaboujaoudeh
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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 ?
 
  • #6
lalbatros
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what is the exact definition of electronegativity ?
 
  • #7
FunkyDwarf
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thirst for negative charge
 
  • #8
lalbatros
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Yes:

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 ...
 
  • #9
eaboujaoudeh
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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
Sankalp Goyal
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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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