1.- Calculate the latice energy of magnesium sulfide from thefollowing data: Mg(

Question

1.- Calculate the latice energy of magnesium sulfide from thefollowing data: Mg(s) ----> Mg(g) + Ho= 148 kJ/mol Mg(g) ----> Mg2+(g) + 2e- Ho= 2186 kJ/mol S8(s) -----> 8S(g) Ho=2232 kJ/mol S(g) + 2e- --->S2-(g)   Ho= 450 kJ/mol 8Mg(s) + S8(s) --->8MgS(s)  Hof= -2744kJ/mol possible answers: a) -3406 kJ/mol    b) -2720kJ/mol    c) 2720 kJ/mol    d) 3406kJ/mol Mg(s) ----> Mg(g) + Ho= 148 kJ/mol Mg(g) ----> Mg2+(g) + 2e- Ho= 2186 kJ/mol S8(s) -----> 8S(g) Ho=2232 kJ/mol S(g) + 2e- --->S2-(g)   Ho= 450 kJ/mol 8Mg(s) + S8(s) --->8MgS(s)  Hof= -2744kJ/mol possible answers: a) -3406 kJ/mol    b) -2720kJ/mol    c) 2720 kJ/mol    d) 3406kJ/mol

Explanation / Answer

8Mg(s) ----> 8Mg(g)                                    Ho= 1184 kJ 8Mg(g) ----> 8Mg2+(g) +16e-                     Ho= 17488 kJ/mol S8(s) ----->8S(g)                                         Ho= 2232 kJ/mol 8S(g) + 16e- ---> 8S2-(g)                                Ho= 3600 kJ/mol 8Mg2+(g) +8S2-(g) ----> 8MgS(s)               Ho=?????????   ---------------------------------------------------------------- 8Mg(s) + S8(s) --->8MgS(s)                        Hof=-2744 kJ/mol Everything in green cancels, that in red does not. The??????????? value is what we must solve for. 1184 kJ + 17488 kJ + 2232 + 3600kJ/mol + ????????? =   -2744 kJ/mol ???????? = -27248 kJ........that's for combining 8 mol of theMgS from the ions. We need it for 1 mole so divide by8: -3406 kJ is released when 1 mol of ions combines to form 1 molof MgS. Fair warning: If you do not work out 2 more of these byyourself to understand the nature of the Born-Haber process and theapplication of Hess's law to such problems, you will fall flat onyour face during an exam on such problems. Remember, starting the with the elements.......... metal is sublimed, metal is ionized nonmetal is sometimes dissociated, then ionized metal ion and nonmetals ions combine (The lattice energycomponent) Each of these have energies associated with them and combinedgive you the formation of the resulting compound from thecorresponding elements in their standard states.

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