How do you calculate lattice energy?

I need help with lattice energy, please?

• Calculate the lattice energy of AgCl using the following data: Ag(s) => Ag(g) ΔH = +284 kJ/mol Ag(g) => Ag+(g) + e- ΔH = +731 kJ/mol Cl2(g) => 2Cl(g) ΔH = +244 kJ/mol Cl(g) + e- => Cl-(g) ΔH = -349 kJ/mol Ag(s) + 1/2 Cl2(g) => AgCl(s) ΔH = -127 kJ/mol I just need to know how to do it STEP BY STEP as simple as you can. I have a test coming up and my professor sucks at explaining it. No need for the answer, just the explanation. Thanks a whole bunch!

• Answer:

  Hi reason no one answered your question is this is definitely easier to answer with a diagram and that on yahoo is a little difficult. So lets try this Get a big piece paper put Ag(s) + 0.5 Cl2(g) 3/4 of the way down on the LHS. Draw an arrow 1 up and write Ag(g) + 0.5cl2(g) On the arrow put the value 284Kj/mol Draw an arrow 2 up from Ag(g) + 0.5cl2(g) to Ag+(g) +0.5Cl2(g) on the arrow put value 731 Kj/mol Draw an arrow3 up from Ag+(g) +0.5Cl2(g to Ag+(g) +Cl(g) on tthearrow put the value 244Kj/mol /2 Draw an arrow 4 DOWN and across so you can see what you are doing from Ag+(g) +Cl(g) to Ag+(g) +Cl-(g) give this tthevalue -349 Draw an arrow 5 Down (down down past the level of Ag(s) +0.5Cl2(g)) from Ag+(g) +Cl-(g) . to AgCl(s). Finally complete by linking up the Ag(s) +0.5Cl2(g) with a ddownwardarrow 6 to AgCl(s). and give this the value -127Kj/mol You should now have a cycle for the system of AgCl with one unknown that is the enthalpy change from Ag+(g) and Cl-(g) to AgCl(s) or arrow 5 Note the value of Arrow 3 which is divided by two because you only need half a mole of Cl2 to produce one mole of silver chloride Arrow 3 = +127+284+731+(244/2)-349= I hope that makes sense if you have a test look up lattice enthalpies in a revision or text book they should have a good diagram. The idea is that you take two components in their normal state you modify them until they are both gaseous ions with all the various enthalpy changes. you then get the standard enthalpy of formation which takes the components in their normal state and makes the solid out of them and so you build a huge Hess's "triangle" except it is not a triangle anymore. You can then work out the Lattice enthalpy which you could never really do experimentally because gaseous ions don't suddenly go from being gaseous ions to a solid lattice. Hope this helps