Ea h cl 697 6 kj mol mg 2 g 2cl g mgcl 2s δ lf h

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ea H Cl = - 697 . 6 kJ / mol Mg 2+ (g) + 2Cl - (g) MgCl 2(s) Δ lf H MgCl 2 Mg (s) + Cl 2(g) MgCl 2(s) Δ f H MgCl 2 = - 641 . 3 kJ / mol Δ f H MgCl 2 = Δ H 1 + Δ H 2 + Δ H 3 + Δ H 4 + Δ lf H MgCl 2 - 641 . 3 kJ / mol = 147 . 1 + 2189 + 242 . 6 + - 697 . 6 kJ / mol + Δ lf H MgCl 2 Δ lf H MgCl 2 = - 2522 kJ / mol
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Some enthalpies of lattice formation Compound r 2 / r 1 Structure Δ lf H / kJ mol - 1 LiF 0.444 NaCl - 1037 NaF 0.744 NaCl - 926 KF 0.964 NaCl - 821 NaCl 0.547 NaCl - 787 KCl 0.762 NaCl - 717 NaBr 0.505 NaCl - 752 BeCl 2 - 3017 MgCl 2 - 2524 CaCl 2 - 2255 MgO 0.514 NaCl - 3850 CaO 0.714 NaCl - 3461
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Compounds you’ll never see NaXe: Xenon has no electron affinity (positive Δ ea H ). Having a negative enthalpy of electronic attraction is generally necessary to make the overall process favorable. NaCl 2 : The second ionization energy of sodium is huge. MgCl: It may be energetically favorable to form this compound from the elements. However, because of the very large enthalpy of lattice formation, MgCl 2 is energetically extremely favorable. Thus, the disproportionation reaction 2MgCl (s) Mg (s) + MgCl 2(s) would be energetically favorable.
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  • Fall '06
  • Marc
  • Enthalpy, Sodium chloride, Standard enthalpy change of formation, Marc R. Roussel, Lattice formation

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