How to calculate lattice energy of magnesium sulfide?

Question

Mg(s) → Mg(g) ΔH° = 148 kJ/molMg(g) → Mg2+(g) + 2e- ΔH° = 2186 kJ/molS8(s) → 8S(g) ΔH° = 2232 kJ/molS(g) + 2e- → S2-(g) ΔH° = 450 kJ/mol 8Mg(s) + S8(s) → 8MgS(s) ΔH°f = -2744 kJ/molMg2+(g) + S2-(g) → MgS(s) ΔH°MgS = ?I’m having trouble because it is 8 moles instead of 1.Thanks for the help!

Francesco Paucek · Accepted Answer

Take the second equation and flip it around. This changes the sign of ΔH°Mg2+(g) + 2e- → Mg(g) ΔH°=-2186 KJ/molflip the fourth equation around. Again only the sign of ΔH° changesS2-(g) → S(g) + 2e- ΔH°=-450 KJ/molDivide the fifth equation by 8. This also divides the value of ΔH° by 8Mg(s) + 1/8S8(s) → MgS(s) ΔH°=-343 KJ/molflip the first equationMg(g) → Mg(s) ΔH°=-148 KJ/molflip the third equation and divide by 8S(g) → 1/8S8(s) ΔH°=-279 KJ/molNow combine all the equations and you should get the desired equation. Add all the values for ΔH° and you get the lattice energy for MgS.Mg2+(g) + S2-(g) → MgS(s) ΔH°MgS=-3406 KJ/mol

Francesco Paucek · Answer

Lattice Energy Of Magnesium Sulfide

Dr. Nina Hettinger I

How to calculate lattice energy of magnesium sulfide?

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