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Topic: Calculating lattice enthalpy  (Read 7925 times)

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Offline superschan

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Calculating lattice enthalpy
« on: September 07, 2007, 12:49:38 PM »
I was given a question where I have to find the lattice enthalpy of CaCl2 and I am given the following:
energy of vapourisation Ca:  192 kJ/mol
Ca 1st ionisation energy: 589.5 kJ/mol
Ca 2nd ionisation energy: 1146 kJ/mol
Cl electron affinity: -348 kJ/mol
Cl2 bond energy: 242.3 kJ/mol
Heat of formation of CaCl2: -795 kJ/mol

I'm used to working with energy of atomization which is not present. I'm guessing energy of vapourisation is the same thing but I have never used bond energy to caculate lattice enthalpy. Should this be added on or subtracted? Below is what I have done:
-795(Heat of formation of CaCl2) = 192(energy of vapourisation Ca) + 589.5(Ca 1st ionisation energy) + 1146(Ca 2nd ionisation energy) - 242.3(Cl2 bond energy) - 2x348(Cl electron affinity) + lattice enthalpy of CaCl2

I got an answer of -1784.2 kJ/mol for the lattice enthalpy of CaCl2 is this correct?

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