We’re being asked to calculate the enthalpy of formation of KCl, given the lattice energy.
Recall that lattice energy is the energy required to combine two gaseous ions into a solid ionic compound:
Mx+(g) + Ny–(g) → MyNx(s)
To calculate for lattice energy, we need to do the Born-Haber cycle for KCl. We start with the corresponding formation equation for KCl:
K(s) + ½ Cl2(g) → KCl(s), ΔH˚f
Use the data given below to construct a Born-Haber cycle to determine the heat of formation of KCl.
|K(g) → K+(g) + e-||418|
|Cl2(g) → 2 Cl(g)||244|
|Cl(g) + e- → Cl-(g)||-349|
|KCl(s) → K+(g) + Cl-(g)||717|
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